EXCHANGE 


BIOLOGY 

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HABIT  FORMATION  IN  A  STRAIN  OF 
ALBINO  RATS  OF  LESS  THAN 
NORMAL  BRAIN  WEIGHT 


A  DISSERTATION 

SUBMITTED  TO  THE  BOARD  OF  UNIVERSITY 
STUDIES  OF  THE  JOHNS  HOPKINS  UNIVERSITY, 
IN  CONFORMITY  WITH  THE  REQUIREMENTS  FOR 
THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY 


By 
GARDNER  CHENEY  BASSET 


1913 


(Reprinted  from  Behavior  Monographs,  Volume  2,  Number  4,  1914) 


HABIT  FORMATION  IN  A  STRAIN  OF 
ALBINO  RATS  OF  LESS  THAN 
NORMAL  BRAIN  WEIGHT 


A  DISSERTATION 

SUBMITTED  TO  THE  BOARD  OF  UNIVERSITY 
STUDIES  OF  THE  JOHNS  HOPKINS  UNIVERSITY. 
IN  CONFORMITY  WITH  THE  REQUIREMENTS  FOR 
THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY 


By 
GARDNER  CHENEY  BASSET 

1918 


(Reprinted  from  Behavior  Monographs,  Volume  2,  Number  4,  1914) 


we      . 

LIBRARY 
G 


CONTENTS 

PAGE 

I.     Introduction 1 

II.    Methods 2 

III.  Experiment  1 :  the  Maze 5 

IV.  Experiment  2:  the  Preliminary  Inclined  Plane 25 

V.     Experiment  3:  the  Inclined  Plane 30 

VI.     Summary  and  Conclusions 43 


m 


291041 


ACKNOWLEDGMENTS      . 

Before  entering  upon  the  body  of  this  presentation  I  desire 
to  express  my  obligations  to  those  without  whose  co-operation 
my  experiments  would  have  been  of  less  value. 

Above  all  am  I  indebted  to  Professor  John  B.  Watson,  Direc- 
tor of  the  Johns  Hopkins  Psychological  Laboratory,  who  has 
kept  himself  informed  of  the  progress  of  my  experimentation 
and  who  has  been  ready  at  all  times  with  helpful  suggestions 
and  encouragement. 

To  Dr.  Henry  H.  Donaldson  I  owe  much:  for  suggesting 
the  experiment;  for  placing  the  facilities  and  materials  of  the 
Wistar  Institute  at  my  disposal;  for  much  helpful  advice  as 
to  the  evaluation  of  my  results. 

To  Dr.  Shinkishi  Hatai  for  preparing  the  anatomical  data 
referring  to  the  rats  used  in  my  experiments. 

To  Dr.  Helen  D.  King  for  keeping  her  sequences  of  in- 
breeding moving  so  perfectly  that  it  was  possible  at  any  time 
to  procure  inbred  rats  of  the  desired  age. 

GARDNER  CHENEY  BASSET. 


IV 


I.    INTRODUCTION 

A  few  years  ago  experimental  inbreeding  of  the  albino  rat, 
Mus  norvegicus  albinus,  was  started  at  the  Wistar  Institute  of 
Anatomy  and  Biology  in  order  to  determine  the  anatomical 
consequences  of  such  procedure  upon  successive  generations  of 
progeny.  Among  other  results  obtained  was  a  distinct  and 
progressive  decrease  in  actual  and  relative  brain  weight  (relative, 
that  is,  in  reference  to  body  length)  for  four  generations  of 
close  inbreeding.  At  the  end  of  the  fourth  generation  the  rats 
seemed  lacking  in  vitality  and,  for  this  reason,  were  subjected 
to  a  change  in  food.  From  this  period  until  the  end  of  the 
tenth  generation  (the  extent  of  inbreeding  at  the  time  this 
paper  was  prepared)  the  relative  brain  weight  remained,  on 
the  average,  constant  at  six  and  one-half  per  cent  less  than  that 
of  the  normal  control  rats. 

When,  early  in  October,  1911,  Dr.  Donaldson  suggested  to 
Professor  Watson  that  the  decrease  in  brain  weight  might  be 
accompanied  by  a  similar  decrease  in  ability  to  form  habits 
a  new  line  of  investigation  in  comparative  psychology  was 
opened  up.  The  problem  was  offered  to  the  writer  and  gladly 
accepted. 

It  is  no  part  of  the  purpose  of  this  paper  to  raise  the  question 
as  to  whether  inbreeding,  per  se,  results  deleteriously  upon  the 
progeny.  In  this,  as  in  all  disputed  questions,  it  is  unsafe  to 
be  arbitrary,  and  authoritative  testimony  must  await  the  results 
of  further  investigations.  We  know,  upon  the  authority  of 
historians,  that  the  Incas  of  Peru  for  many  generations  married 
their  sisters  and  were  physically  and  mentally  superior  to  their 
subjects.  Breeders  of  domestic  animals  frequently  resort  to 
inbreeding  in  order  to  perfect  desirable  qualities  in  the  strain. 
It  may  be,  as  many  claim,  that  inbreeding  results  deleteriously 
only  in  cases  where  an  hereditary  taint,  occurring  in  the  common 
ancestor,  is  strengthened  in  the  progeny  of  a  consanguineous 
union.  Of  the  rats  used  in  the  experiments  hereinafter  described, 
it  is  not  postulated  that  the  lesser  ability  to  form  habits  is  neces- 
sarily due  either  to  inbreeding  or  to  the  environmental  factor  of 


2  GARDNER  CHENEY  BASSET 

insufficient  nourishment  during  the  first  four  generations;  but, 
the  rats  used  for  purposes  of  inbreeding  produced  a  strain  hav- 
ing a  lesser  relative  brain  weight  on  the  average.  This  strain 
of  rats  I  shall  hereafter,  for  convenience,  refer  to  as  the  Inbred 
Strain.  The  object,  then,  of  the  following  experiments  is  to 
compare  the  habit-forming  ability  of '  the  inbred  strain  with 
lesser  brain  weights,  with  the  ability  of  a  normal  control  series. 

Owing  to  the  fact  that  experimental  work  on  the  brain  weight 
problem  has  not  before  been  attempted  there  is  no  history  and 
little  literature  to  be  presented.  Donaldson1  reproduces  tables 
from  Manouvrier2  showing  the  brain  weights  of  eminent  men 
to  be,  on  the  average,  greater  than  those  of  average  Parisians. 
It  is  not  necessarily  true  that  the  specific  individual  with  greater 
brain  weight  is  more  intelligent  or  will  contribute  more  to  the 
world's  arts  and  sciences  than  the  specific  individual  of  lesser 
brain  weight;  but,  if  the  conclusions  of  Manouvrier  are  to  be 
believed,  individuals  of  brain  weight  above  the  average  are 
more  liable  to  be  of  superior  intelligence  and  to  do  the  world 
greater  service. 

The  results  of  the  experiments  described  in  this  paper  agree 
closely  with  Manouvrier 's  conclusions.  Tables  of  distribution 
of  brain  weights  of  the  inbred  strain  and  normal  control  series 
overlap;  but  the  normal  series,  having  a  greater  brain  weight 
average,  show  greater  ability  tin  habit  formation. 

All  the  experiments  here  described  were  carried  out  at  the 
Psychological  Laboratory  of  the  Johns  Hopkins  University. 

II.    METHODS 

All  the  inbred  rats  used  in  this  investigation  were  bred  at 
the  Wistar  Institute  of  Anatomy  and  Biology  by  Dr.  Helen 
D.  King.  Two  strains  were  used,  referred  to  in  this  paper  as 
strains  A  and  B.  The  original  parents  of  each  strain  were  taken 
at  random,  a  male  and  female  from  each  of  two  unrelated  lit- 
ters. The  A  male  was  mated  to  his  sister,  A  female,  and  the 
B  male  to  his  sister,  B  female.  Their  respective  litters  consti- 
tuted generation  1A  and  IB.  From  this  point  inbreeding  was 
carried  on  by  selecting  from  the  litter  the  healthiest  appearing 

1  Donaldson:    The  Growth  of  the  Brain.     London  and  New  York,   1909,  pp. 
128  ff. 

2  Manouvrier,  Sur  Interpretation  de  la  quantite  dans  1'enc^phale,  etc.,  Paris,  1885. 


HABIT  FORMATION  IN  ALBINO  RATS  3 

rats  and  mating  brother  to  sister  within  the  same  litter,  this 
constituting  the  closest  possible  inbreeding.  At  about  thirty 
days  of  age  the  young  rats  were  taken  from  their  mother,  and 
those  to  be  used  by  the  writer  were  shipped  to  the  Johns  Hop- 
kins University.  There  were  no  fatalities  in  transit  and  all 
arrived  apparently  in  good  condition.  The  system  of  number- 
ing individual  rats  for  identification  was  as  follows:  the  first 
number  referred  to  the  generation  of  inbreeding,  the  letter 
(  A  or  B)  to  the  strain,  and  the  last  number  was  that  applied 
to  the  individual.  For  example,  7A90?  may  be  analyzed  as 
follows:  7th  generation  inbred,  A  strain,  individual  90,  female. 
Each  rat  had  one  or  both  ears  punched  or  clipped  to  agree  with 
the  individual  number,  a  system  in  use  by  Professors  Castle 
and  Yerkes  at  the  Harvard  laboratories. 

It  seemed  advisable  to  secure  normal  control  mating  strains 
from  different  laboratories  in  order  to  avoid  any  possibility  of 
inbreeding.  In  addition  to  our  own  Hopkins  stock  there  were 
obtained  rats  from  the  Wistar  Institute,  Columbia  University, 
animal  dealers  in  Baltimore,  and  from  Dr.  Herbert  M.  Evans 
of  the  Johns  Hopkins  Medical  School.  Care  was  taken  in  mat- 
ing the  control  series  to  avoid  any  approach  to  inbreeding.  As 
in  the  case  of  inbred  rats  the  young  were  taken  from  the  mother 
at  the  age  of  thirty  days.  The  system  of  numbering  individual 
control  rats  for  identification  was  as  follows:  the  first  letter,  S, 
signified  that  it  was  a  standard  or  normal  control  rat,  letters 
within  parentheses  gave  the  pedigree,  and  the  figures  gave  the 
individual  number.  For  example,  S(C/EB)70c^  may  be  analyzed 
as  follows:  standard,  or  normal  control  series,  Columbia  father, 
Hopkins  Medical  maternal  grandfather,  maternal  grandmother 
purchased  from  a  Baltimore  dealer,  individual  70,  male.  The 
same  system  of  ear  marking  was  used  as  in  the  case  of  the 
inbred  rats. 

When  taken  from  the  mother  males  and  females  were  kept 
in  separate  cages.  According  to  Watson3  the  bearing  of  young 
has  some  effect  upon  the  central  nervous  system  of  the  white 
rat;  for  this  reason,  and  in  order  to  keep  conditions  constant, 
neither  males  nor  females  used  in  these  experiments  were  al- 
lowed to  mate.  As  solitude  may  be  a  factor  affecting  behavior, 

3  Watson:  The  Effect  of  the  Bearing  of  Young  Upon  the  Body- Weight  and  the 
Weight  of  the  Central  Nervous  System  of  the  Female  White  Rat.  Journ.  of  Comp. 
Neur.  and  Psych.,  Vol.  XV.,  No.  6,  1905. 


4  GARDNER  CHENEY  BASSET 

from  three  to  five  rats  were  kept  in  each  cage,  the  cages  being 
made  sufficiently  large  (24"  x  15"  x  15")  to  permit  it.  Cages 
were  frequently  disinfected  with  a  preparation  the  principal 
ingredient  of  which  is  carbolic  acid.  The  rats  were  occasionally 
immersed  in  a  solution  of  this  preparation  in  order  to  destroy 
skin  parasites.  A  layer  of  clean  chips  and  shavings  was  kept 
on  the  floor  of  all  cages.  The  food,  from  the  time  of  weaning, 
consisted  of  bread  soaked  in  milk  every  day,  grain  and  sun- 
flower seeds  twice  a  week,  and  banana  or  carrot  once  a  fort- 
night. Temperature  was  kept  as  uniformly  as  possible  at 
70°  F.  In  order  to  facilitate  this  a  small  gas  heater  was 
installed  and  it  proved  very  efficient  even  during  the  coldest 
days  of  winter.  As  the  animal  laboratory  is  located  in  the 
basement  the  temperature,  during  the  summer,  rarely  rose 
above  our  norm. 

At  the  age  of  sixty  days  the  rats  intended  for  experimental 
purposes  were  placed  on  a  short  allowance  .of  feeding  time 
(thirty  minutes)  in  order  to  prepare  them  for  experimentation. 
The  experiments  were  begun  with  both  inbreds  and  normal 
control  at  the  age  of  seventy  days.  Care  was  taken  in  each 
experiment  to  use  the  same  number  of  males  and  females  in 
the  control  series  as  in  the  inbred;  this  was  necessary  because, 
as  in  man,  the  relative  brain  weight  of  the  female  is  greater  than 
that  of  the  male.  Experiments  upon  individual  rats  were  con- 
ducted as  nearly  as  possible  at  the  same  time  of  day,  both  to 
form  feeding  rhythms  and  in  order  not  to  interfere  with  other 
rhythms. 

There  are  three  methods  of  estimating  perfection  in  experi- 
ments relating  to  the  habit-forming  abilities  of  animals:  the 
number  of  errors,  the  distance  traversed,  the  time  consumed. 
It  is  hard,  in  any  case,  to  form  a  judgment  as  to  what  consti- 
tutes an  error  in  the  behavior  of  an  animal;  especially  is  this 
true  in  a  comparative  study  of  this  kind  where  it  is  possible 
for  the  personal  prejudices  of  the  experimenter  to  become  a 
factor.  At  the  time  this  investigation  was  begun  there  was  no 
adequate  means  of  measuring  the  distance  traversed.  This  left 
at  the  disposal  of  the  experimenter  but  one  criterion:  the  time 
consumed.  However,  time  consumed  in  learning  is  the  criterion 
most  frequently  used  by  experimenters  in  the  animal  field. 


HABIT  FORMATION  IN  ALBINO  RATS  5 

Hicks,4  in  summing  up  the  experimental  results  of  several  in- 
vestigators, concludes  that  "  time  is  the  best  single  criterion, 
inasmuch  as  it  represents  all  phases  of  the  process  of  learning, 
and  since  it  will  yield  the  most  comparable  results  at  the  hands 
of  different  investigators."  In  timing  the  rats  a  very  accurate 
Swiss  split-second  stopwatch  was  used.  Under  ideal  conditions, 
perhaps,  the  animal  should  be  presented  to  the  problem  by  one 
person,  timed  by  another,  while  the  experimenter  himself  should 
merely  record  the  results.  But  timing  very  soon  becomes  auto- 
matic; when  the  rat  is  crossing  the  line  it  is  almost  impossible 
to  inhibit  the  impulse  to  press  the  stem  of  the  watch. 

At  the  conclusion  of  the  experiments  all  the  rats  were  shipped 
to  the  Wistar  Institute  where  Dr.  Shinkishi  Hatai  ascertained 
the  anatomical  data  necessary  for  the  formulation  of  the  com- 
parison between  relative  brain  weight  and  the  ability  to  form 
habits. 

III.    EXPERIMENT   1:    THE  MAZE 

The  apparatus  used  in  this  experiment  was  the  Watson  Maze 
(see  Plate  I) .  This  maze  is  circular  in  form,  five  feet  in  diameter, 
with  entrances  from  outer  runways  to  the  next  inner  at  alternate 
ends  of  a  quadrant  arc.  The  runways  are  each  four  inches  wide, 
and  the  centre,  F,  eight  inches  in  diameter.  The  partitions  are 
of  aluminum  and  rise  to  a  height  of  five  inches  above  the  floor 
of  the  maze.  A  heavy  wire  screen  resting  on  the  top  serves 
the  purpose  of  preventing  the  rats  from  climbing  over  the  par- 
titions, and  also  allows  the  experimenter  to  observe  all  move- 
ments within.  The  perfect  course  of  the  animal  running  is, 
from  the  entrance,  E,  through  runway  entrances  1,  2,  3,  4,  5, 
6,  and  7  to  F  (food).  Each  side  of  runway  entrances  2  to  6 
inclusive  lead  into  cul-de-sacs. 

The  object  of  the  experiment  was  to  have  each  rat  learn  to 
reach  the  centre,  F,  in  the  least  possible  time,  the  starting  time 
being  taken  when  the  animal  crossed  runway  entrance  1,  and 
the  finishing  time  when  he  crossed  entrance  7. 

In  preparation,  each  animal,  beginning  at  the  age  of  sixty- 
five  days,  was  fed  alone  in  the  centre,  F,  ten  minutes  daily  for 

4  Hicks,  The  Relative  Values  of  the  Different  Curves  of  Learning.  Jour. 
Animal  Behavior.,  Vol.  I,  pp.  138  ff. 


GARDNER  CHENEY  BASSET 


The  Uratson  ftlaje. 
Plate  I. 


HABIT  FORMATION  IN  ALBINO  RATS  7 

five  consecutive  clays.  During  this  period  the  centre  was  barred 
from  the  rest  of  the  maze  at  entrance  6.  At  the  age  of  seventy 
days  the  experiment  began.  Eleven  males  and  ten  females 
from  the  inbred  strain  were  used  and,  as  control,  an  equal  num- 
ber of  males  and  females  from  the  normal  control  series.  Of 
the  inbred  rats,  fourteen  were  from  the  sixth  generation  and 
seven  from  the  seventh.  The  stimulus  used  was  the  food  to 
which  they  had  become  accustomed,  bread  soaked  in  milk. 

From  the  beginning  of  the  experiment  each  rat  was  required 
to  run  from  E  to  F  five  times  daily.  At  the  end  of  the  fifth  trial 
it  was  allowed  to  feed  in  the  centre,  F,  for  five  minutes,  but 
permitted  no  more  food  until  the  completion  of  the  next  day's 
experiment.  Each  rat  was  used  daily  until  it  had  learned  the 
course  perfectly,  the  criterion  of  perfection  being  five  perfect 
trials  for  each  of  three  successive  days.  A  perfect  trial  consisted 
in  running  the  course  within  six  seconds,  a  period  of  time  so 
short  that  it  was  practically  impossible  for  the  rat  to  make  a 
detectable  error  and  reach  the  centre  within  that  time.  Those 
rats  failing  to  learn  within  one  hundred  days  (five  hundred 
trials)  were  no  longer  used  for  experimentation.  Such  rats  as 
learned  the  maze  were,  at  the  conclusion  of  the  experimentation, 
fed  for  sixty  days  in  a  runway  twenty-five  feet  long  with  a  feed- 
ing-box at  the  right  of  the  far  end.  At  the  end  of  this  period 
they  were  tested  for  retention  and  relearning. 

The  shortest  period  of  time  required  by  an  inbred  rat  to 
learn  the  maze  perfectly  was  twelve  days;  for  a  control  rat, 
ten  days.  Two  inbred  rats  and  one  control  failed  to  learn  the 
maze  habit  within  the  one  hundred  days  allowed.  During  the 
process  of  learning  certain  of  the  normal  control  series  showed 
peculiarities  of  behavior  similar  to  those  exhibited  by  the  inbred 
strains.  These  peculiarities,  for  the  greater  part,  consisted  in 
disorientation  and  persistent  errors.  All  the  normal  control 
series,  with  the  exception  of  five  rats  containing  germ-plasm  of 
the  B  strain,  had  perfected  the  maze  habit  by  the  twenty-fourth 
day.  The  control  rat  mentioned  above  as  having  failed  to  learn 
the  maze  within  one  hundred  days  was  from  this  group.  So 
erratic  in  behavior  and  so  slow  in  learning  were  the  B  strain 
rats  that  the  investigator  suspected  them  to  be  of  less  than 
normal  brain  weight;  and,  when  the  returns  were  received  from 
the  Wistar  Institute,  this  was  indeed  found  to  be  the  case. 


8  GARDNER  CHENEY  BASSET 

For  greater  convenience  in  making  a  comparative  study,  I 
have  placed  together  in  Table  I  a  summary  consisting  of  the 
daily  averages  of  the  entire  inbred  group  and,  directly  beneath, 
the  corresponding  daily  averages  of  the  entire  normal  control 
group.  From  this  table,  too,  are  constructed  the  comparative 
curves  of  learning. 

Table  I  compares:  (a)  the  progress  of  learning  by  days; 
(b)  the  '  'absolute  retention"  (this  being  a  term  used  here  to 
represent  the  time  required  to  complete  the  first  trial  of  the 
relearning  series  after  the  sixty  days'  rest;  the  greater  the  re- 
tention, the  less  is  the  time) ;  (c)  the  progress  of  relearning  by 
days;  (d)  the  anatomical  data. 

Table  la  shows  that  two  of  the  inbred  and  one  of  the  control 
rats  (the  latter  from  the"  B  strain)  failed  to  learn  the  maze  habit. 
The  inbreds  required,  on  the  average,  36.62+  days  to  learn; 
the  control  but  24.67+  days.  The  absolute  retention  of  the 
inbred  rats  (Table  Ib)  was,  on  the  average,  81.558  seconds; 
of  the  control  series,  59.640  seconds.  The  two  inbreds  and  one 
control  failing  to  learn  the  maze  were  not,  of  course,  tested  for 
retention  and  relearning.  Of  the  inbreds  so  tested  (Table  Ic), 
two  failed  to  relearn  within  fifty  days,  in  consequence  of  which 
it  was  thought  useless  to  carry  them  further.  All  the  control 
series  had  relearned  at  the  end  of  twenty-two  days.  The  inbreds 
required,  on  the  average,  12.68+  days  to  relearn;  the  normals 
but  5.75  days. 

In  all  these  criteria  of  ability:  learning,  absolute  retention, 
and  relearning,  the  rats  of  the  normal  control  series  are  shown, 
on  the  average,  to  be  superior  to  those  of  the  inbred  series. 

There  are  two  methods  in  use  for  estimating  the  relative 
brain  weight:  in  reference  to  body  length  and  in  reference  to 
body  weight.  In  a  healthy  normal  rat  the  difference  between 
body  weight  in  grams  and  body  length  in  millimeters  is  slight; 
but,  under  conditions  of  overfeeding,  underfeeding,  or  of  sick- 
ness the  body  weight  varies  greatly  while  the  body  length 
remains  constant.  For  this  reason  Dr.  Donaldson  of  the  Wistar 
Institute  has  accepted  body  length  as  the  better  method.  I 
have  laid  greater  stress  on  the  body  length  criterion,  although 
both  are  presented  in  the  tables  of  anatomical  data.  Both 
body  length  and  body  weight  of  the  inbred  rats  used  in  the 
maze  (Table  Id)  are,  on  the  average,  slightly  greater  than  is 


HABIT  FORMATION  IN  ALBINO  RATS 


9 


the  case  with  the  normal  controls.  The  relative  brain  weight 
(in  reference  to  body  length)  of  the  inbreds  is  4.43%  less  than 
that  of  the  normals.  The  relative  brain  weight  (in  reference 
to  body  weight)  of  the  inbreds  is  7.99%  less  than  that  of  the 
normal  control.  The  percentage  of  water  in  brain  and  cord 
normally  decreases  with  age ;  but  in  the  inbreds  used  in  the  maze 
experiment,  although  killed,  on  the  average,  fourteen  days  later 
than  the  control  rats,  the  percentage  of  water  was  greater. 

The  figures  presented  in  Table  I  support  the  hypothesis  that 
a  less  than  normal  average  brain  weight  in  a  strain  of  rats  is 
accompanied  by  an  average  lesser  ability  to  form  habits. 


TABLE    la 
THE  MAZE 

DAILY  LEARNING  AVERAGES  OF  INBRED  AND  NORMAL  CONTROL  RATS 
(Time  in  seconds) 


Inbred  Average 531 .665 

Control  Average 505 . 128 


Inbred  Average. , 
Control  Average 


Inbred  Average . 
Control  Average . 


Inbred  Average . 
Control  Average , 


Inbred  Average . . 
Control  Average. 

Inbred  Average . , 
Control  Average . 

Inbred  Average . . 
Control  Average . 

Inbred  Average. 
Control  Average . 

Inbred  Average . 
Control  Average , 


Day    1 

31.665 
05.128 

Day    2 

91.404 
110.739 

Day    3 

68.160 
53.851 

Day    4 
39.459 

28.404 

Day    5 

25.568 
25.613 

Day    6 

20.015 
17.366 

Day    7 
13.899 

13.381 

Day    8 
11.061 
11.994 

Day    9 

9.709 
12.440 

Day  10 
9.522 

9.619 

Day  11 

10.217 
7.295 

Day  12 

7.937 
7.748 

Day  13 

8.708 
7.354 

Day  14 

7.600 
6.904 

Day  15 

7.000 
7.277 

Day  16 
6.439 

6.687 

Day  17 
6.585 

6.428 

Day  18 
6.305 

5.900 

Day  19 
6.492 

6.209 

Day  20 

6.458 
5.851 

Day  21 

6.362 
5.630 

Day  22 

5.749 
5.  $16 

Day  23 

5.978 
5.710 

Day  24 

5.753 
5.675 

Day  25 
6.248 

5.420 

Day  26 
5.734 

5.389 

Day  27 
7.130 

5.442 

Day  28 
5.669 

5.479 

Day  29 
6.387 

5.496 

Day  30 

5.697 
5.437 

Day  31 

5.384 
5.700 

Day  32 

5.708 
5.502 

Day  33 

5.702 
5.378 

Day  34 

'  6.084 
5.499 

Day  35 

5.731 
5.308 

Day  36 

5.590 
5.272 

Day  37 
5.476 

5.249 

Day  38 

5.494 
5.327 

Day  39 

5.540 
5.363 

Day  40 
5.848 

5.316 

Day  41 
5.640 

5.343 

Day  42 
5.978 

5.573 

Day  43 

5.631 
5.375 

Day  44 
5.526 

5.250 

Day  45 
13.456 

5.444 

10 


GARDNER  CHENEY  BASSET 


Day  46 

Day  47 

Day  48            Day  49 

Day  50 

Inbred  Average  

6.734 

7.400 

6.602          5.713 

5.840 

Control  Average  

5.282 

5.162 

5.147          5.198 

5.223 

Day  51 

Day  52 

Day  53            Day  54 

Day  55 

Inbred  Average  

5.844 

5.522 

5.353          5.416 

5.707 

Control  Average  

5.322 

5.360 

5.192          5.615 

5.261 

Day  56 

Day  57 

Day  58            Day  59 

Day  60 

Inbred  Average  

5.924 

5.640 

5.458          5.621 

6.740 

Control  Average  

5.286 

5.181 

5.358          5.286 

5.257 

Day  61 

Day  62 

Day  63            Day  64 

Day  65 

Inbred  Average  

8.347 

6.442 

6.177          5.425 

5.686 

Control  Average  

5.398 

5.952 

5.743          5.299 

5.288 

Day  66 

Day  67 

Day  68            Day  69 

Day  70 

Inbred  Average  

5.88U 

0.630 

5.442          5.821 

5.396 

Control  Average  

5.345 

5.339 

5.173          5.360 

5.223 

Day  71 

Day  72 

Day  73            Day  74 

Day  75 

Inbred  Average  

5.419 

5.737 

5.457          5.587 

5.928 

Control  Average  

5.244 

5.170 

5.130          5.206 

5.110 

Day  76 

Day  77 

Day  78            Day  79 

Day  80 

Inbred  Average  

5.686 

5.798 

5.817          5.627 

5.432 

Control  Average  

5.183 

5.288 

5.170          5.143 

5.421 

Day  81 

Day  82 

Day  83            Day  84 

Day  85 

Inbred  Average  

6.095 

7.335 

5.379          5.535 

6.345 

Control  Average  

5.263 

5.236 

5.211          5.208 

5.160 

Day  86 

Day  87 

Day  88            Day  89 

Day  90 

Inbred  Average  

5.495 

5.316 

5.560          5.421 

7.290 

Control  Average  

5.288 

5.156 

.5.181          5.152 

5.152 

Day  91 

Day  92 

Day  93            Day  94 

Day  95 

Inbred  Average  

5.829 

7.015 

6.204             6.011 

5.556 

Control  Average  

5.257 

5.095 

5.141          5.210 

5.166 

Day  96 

Day  97 

Day  98            Day  99 

Day  100 

Inbred  Average  

5.893 

5.665 

6.017          5.973 

5.958 

Control  Average  

5.217 

5.149 

5.118          5.187 

5.215 

, 

Failed 

Days  required 

to  learn 

to  learn 

Inbr  d  Average  ,  . 

2 

36.62+ 

Control  Average 

1 

24.67+ 

TABLE    Ib 

THE  MAZE 

AVERAGE  ABSOLUTE  RETENTION  OF  INBRED  AND  NORMAL  CONTROL  RATS 

Absolute  Retention 
after  60  days'  rest 

Inbred  Average 81 . 558   seconds 

Control  Average 59 . 640   seconds 


HABIT  FORMATION  IN  ALBINO  RATS 


11 


TABLE    Ic 
THE  MAZE 

DAILY  RELEARNING  AVERAGES  OF  INBRED  AND  NORMAL  CONTROL  RATS 
(Time  in  seconds) 


Day    1 

Day    2 

Day    3 

Day    4 

Day    5 

Inbred  Average  

35.415 

12.208 

10.069 

9.560 

8.069 

Control  Average  

28.574 

18.752 

9.530 

7.996 

6.548 

Day    6 

Day    7 

Day    8 

Day    9 

Day  10 

Inbred  Average  

7.672 

7.659 

6.642 

6.232 

6.604 

Control  Average  

7.076 

6.064 

5.922 

5.670 

5.630 

Day  11 

Day  12 

Day  13 

Day  14 

Day  15 

Inbred  Average  

6.200 

5.966 

6.067 

5.660 

5.587 

Control  Average  

5.508 

5.434 

5.430 

5.414 

5.468 

Day  16 

Day  17 

Day  18 

Day  19 

Day  20 

Inbred  Average  

5.634 

5.669 

5.680 

6.029 

5.718 

Control  Average  

5.970 

5.424 

5.490 

5.354 

5.440 

Day  21 

Day  22 

Day  23 

Day  24 

Day  25 

Inbred  Average  

6.046 

5.834 

5.844 

6.061 

5.771 

Control  Average  

5.614 

5.300 

5.300 

5.300 

5.300 

Day  26 

Day  27 

Day  28 

Day  29 

Day  30 

Inbred  Average  

6.166 

5.697 

5.914 

5.842 

5.817 

Control  Average  

5.300 

5.300 

5.300 

5.300 

5.300 

Day  31 

Day  32 

Day  33 

Day  34 

Day  35 

Inbred  Average  

5.901 

5.905 

5.640 

5.846 

5.939 

Control  Average  

5.300 

5  300 

5.300 

5.300 

5.300 

Day  36 

Day  37 

Day  38 

Day  39 

Day  40 

Inbred  Average  

5.920 

5.956 

5.903 

5.766 

5.726 

Control  Average  

5.300 

5.300 

5.300 

5.300 

5.300 

Day  41 

Day  42 

Day  43 

Day  44 

Day  45 

Inbred  Average  

5.657 

5.848 

5.779 

5.745 

5.861 

Control  Average  

5.300 

5.300 

5.300 

5.300 

5.300 

Day  46 

Day  47 

Day  48 

Day  49 

Day  50 

Inbred  Average  

6.032 

5.815 

5.920 

5.762 

5.697 

Control  Average  

5.300 

5.300 

5.300 

5.300 

5.300 

Failed 

Days 

required 

to  relearn 

to  relearn 

Inbred  Average 

2 

12 

.68  + 

Control  Average 

0 

5 

.75 

TABLE   Id 

THE  MAZE 

ANATOMICAL  DATA  OF  INBRED  AND  NORMAL  CONTROL  RATS 


Inbred  Average  
Control  Average  .  . 

Body             Body            Brain 
Length         Weight         Weight 
in  mm.         in  grms.       in  grms. 
.   195.38          180.55          1.71122 
191.00          171.41          1.74930 

Cord            Water 
Weight        in   Brain 
in  grms.         per  cent 
.52852          78.497 
.52740          78.319 

Inbred  Average 

Water             Per  cent 
in  Cord       Brain  Weight 
per  cent       in  Relation  to 
Body  Length 
71  723                87685 

Per  cent            Age 
Brain  Weight       killed 
in  Relation  to       Days 
Body  Weight 
97052            200 

Control  Average.  . 

.  71.666              .91745 

1.05479            186 

12  GARDNER  CHENEY  BASSET 

In  Plate  II  is  shown  the  curve  of  learning  (below)  and  of 
relearning  (above)  of  the  inbred  rats  compared  with  those  of 
the  normal  control.  These  curves  are  constructed  from  figures 
given  in  Table  I.  The  curve  of  the  inbred  rats  is  indicated  by 
the  solid  line,  that  of  the  normal  control  by  the  broken  line. 
The  ordinates  give  the  average  daily  time  in  seconds  for  each 
group,  and  the  abscissae  the  number  of  the  day  in  which  such 
time  was  made.  The  time  required  by  both  inbred  and  control 
rats 'for  the  first  four  days  was  so  long  that  it  is  represented 
here  by  figures  and  does  not  appear  in  the  curve.  For  the  first 
few  days  the  descent  in  time  for  both  the  inbreds  and  the  con- 
trol is  very  rapid.  From  the  twentieth  day  the  curve  of  the 
control  rats  lies  entirely  below  the  six-second  mark.  The  curve 
of  the  inbred  rats  never  reaches  even  an  approximately  flattened 
appearance,  but  exhibits  great  irregularities,  particularly  on  the 
forty-fifth,  sixty-first,  eighty-second,  ninetieth  and  ninety- 
second  days.  The  inbreds'  curve  of  relearning  is  more  similar 
to  that  of  the  controls,  but  it  must  be  borne  in  mind  that  the 
two  inbreds  and  one  control  rat  that  failed  to  learn  the  maze 
are  not  represented  in  the  relearning  curve,  and  for  this  reason 
this  curve  applies  to  selected  groups.  From  the  twenty-second 
day  the  control  curve  of  relearning  is  perfectly  flat  at  5.3  seconds, 
all  the  control  rats  having  relearned.  Two  of  the  inbred  rats 
having  failed  to  relearn,  their  curve  of  relearning  remains  slightly 
irregular  and  above  that  of  the  control  in  time. 

In  Plate  III  may  be  seen  the  curves  representing  the  distri- 
bution of  learning  and  relearning  of  both  inbreds  and  control 
for  the  maze  experiment.  The  time  is  given  in  days — in  groups 
of  five  for  learning,  in  groups  of  two  for  relearning.  As  may 
readily  be  seen,  the  advantage  from  the  standpoint  of  time 
(days  required  to  learn  and  relearn)  lies  wholly  in  favor  of 
the  normal  control  group. 

The  question  arises  as  to  whether  the  later  generations  of 
inbred  rats  differ  from  the  earlier  in  the  ability  to  form  habits; 
that  is,  is  decrease  in  this  ability  progressive  even  if,  as  earlier 
stated,  decrease  in  relative  brain  weight  after  the  4th  genera- 
tion is  not.  Of  the  inbred  rats  used  in  the  maze  experiment, 
fourteen  were  from  the  6th  generation  and  seven  from  the  7th 
generation.  In  Table  II  is  presented  a  comparative  summary 
consisting  of  the  daily  averages  of  the  6th  and  7th  generation 


HABIT  FORMATION  IN  ALBINO  RATS 


13 


14 


GARDNER  CHENEY  BASSET 


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HABIT  FORMATION  IN  ALBINO  RATS  15 

inbred  rats  used  in  this  experiment.  Two  of  the  7th  generation 
failed  to  learn  the  maze;  all  the  6th  generation  had  learned  it 
after  eighty-three  days.  The  6th  generation  required,  on  the 
average,  32.93  days  in  which  to  learn;  the  7th  generation,  44.00  + 
days.  The  absolute  retention  of  the  6th  generation  was,  on  the 
average,  65.443  seconds;  of  the  7th  generation,  126.680  seconds. 
Two  of  the  6th  generation  failed  to  relearn;  all  the  7th  genera- 
tion had  relearned  at  the  end  of  fourteen  days.  The  6th  genera- 
tion required,  on  the  average,  14.14+  days  to  relearn;  the  7th 
generation  but  8.60  days. 

In  these  criteria  of  ability,  the  6th  generation  excelled  in 
learning  and  absolute  retention;  the  7th  in  relearning.  It  must 
be  remembered,  however,  that  the  7th  generation  rats  used  in 
the  relearning  test  formed  a  selected  group,  the  two  rats  having 
failed  to  learn  having  been  from  this  generation.  On  the  whole, 
the  ability  of  the  7th  generation  inbreds  in  the  maze  experiment 
appears  to  be  somewhat  inferior  to  that  of  the  6th  generation. 

The  body  length  and  body  weight  of  the  6th  generation  aver- 
age greater  than  those  of  the  7th.  The  average  actual  brain 
weight  of  the  6th  generation  is  greater  than  that  of  the  7th. 
The  relative  brain  weight  (in  reference  to  body  length)  of  the 
6th  generation  is  .91%  less  than  that  of  the  7th  generation. 
The  relative  brain  weight  (in  reference  to  body  weight)  of  the 
6th  generation  is  1.50%  less  than  that  of  the  7th  generation. 
The  relative  brain  weight  of  the  inbred  rats  used  in  the  maze 
has  not  decreased  from  one  generation  to  the  next;  but  all  the 
7th  generation  rats  were  females,  and  the  females  normally 
have  relatively  greater  brain  weights  than  the  males.  The 
percentage  of  water  in  brain  and  cord  is  within  .03%  of  the 
same  figure  in  the  two  generations. 

TABLE   Ha 
THE  MAZE 

DAILY  LEARNING  AVERAGES  OF  SIXTH  AND  SEVENTH  GENERATION  INBRED  RATS 

(Time  in  seconds) 

Day    1  Day    2  Day    3  Day    4  Day    5 

Sixth  Average 541.423        73.343        79.997        37.449        30.014 

Seventh  Average 512.149      127.526        44.486        43.480        16.674 

Day    6  Day    7  Day    8  Day    9  Day  10 

Sixth  Average 24.457        16.371         10.646        10.486          9.789 

Seventh  Average 11.131          8.954        11.891          8.154          8.989 


16 


GARDNER  CHENEY  BASSET 


TABLE   Ha—  (Continued) 

Day  11 

Day  12 

Day  13 

Day  14 

Day  15 

Sixth  Average  

11.157 

8.294 

9.825 

7.958 

7.130 

Seventh  Average  

8.337 

7.223 

6.760 

6.926 

6.741 

Day  16 

Day  17 

Day  18 

Day  19 

Day  20 

Sixth  Average  

6.767 

6.690 

6.350 

6.376 

6.421 

Seventh  Average  

5.781 

6.376 

6.216 

6.724 

6.530 

Day  21 

Day  22 

Day  23 

Day  24 

Day  25 

Sixth  Average  

6.276 

5.741 

5.899 

5.576 

6.004 

Seventh  Average  

6.536 

5.764 

6.136 

6.107 

6.736 

Day  26 

Day  27 

Day  28 

Day  29 

Day  30 

Sixth  Average  

5.604 

5.716 

5.455 

5.441 

5.466 

Seventh  Average  

5.993 

9.959 

6.096 

8.279 

6.159 

Day  31 

Day  32 

Day  33 

Day  34 

Day  35 

Sixth  Average  

5.320 

5.674 

5.594 

5.658 

5.464 

Seventh  Average  

5.513 

5.776 

5.919 

6.936 

6.267 

Day  36 

Day  37 

Day  38 

Day  39 

Day  40 

Sixth  Average  

5.406 

5.444 

5.284 

5.316 

5.236 

Seventh  Average  

5.959 

5.541 

5.913 

5.987 

7.073 

Day  41 

Day  42 

Day  43 

Day  44 

Day  45 

Sixth  Average  

5.399 

5.853 

5.396 

5.261 

5.461 

Seventh  Average  

6.124 

6.227 

6.101 

6.056 

29.444 

Day  46 

Day  47 

Day  48 

Day  49 

Day  50 

Sixth  Average  

5.364 

5.259 

5.361 

5.396 

5.387 

Seventh  Average  

9.473 

11.684 

9.084 

6.347 

6.747 

Day  51 

Day  52 

Day  53 

Day  54 

Day  55 

Sixth  Average  

5.713 

5.447 

5.230 

5.244 

5.647 

Seventh  Average  

6.107 

5.673 

5.599 

5.759 

5.827 

Day  56 

Day  57 

Day  58 

Day  59 

Day  60 

Sixth  Average  

5.336 

5.359 

5.301 

5.210 

5.241 

Seventh  Average  

7.101 

6.204 

5.770 

6.444 

9.736 

Day  61 

Day  62 

Day  63 

Day  64 

Day  65 

Sixth  Average  

5.333 

5.366 

5.312 

5.198 

5.209 

Seventh  Average  

14.376 

8.593 

7.907 

5.879 

6.639 

Day  66 

Day  67 

Day  68 

Day  69 

Day  70 

Sixth  Average  

5.198 

5.264 

5.186 

5.286 

5.166 

Seventh  Average  

7.244 

6.364 

5.953 

6.890 

5.856 

Day  71 

Day  72 

Day  73 

Day  74 

Day  75 

Sixth  Average  

5.158 

5.184 

5.192 

5.158 

5.212 

Seventh  Average  

5.941 

6.844 

5.987 

6.444 

7.359 

Day  76 

Day  77 

Day  78 

Day  79 

Day  80 

Si  th  Average  

5.249 

5.189 

5.209 

5.269 

5.169 

Seventh  Average  

6.559 

7.016 

7.033 

6.341 

5.959 

Day  81 

Day  82 

Day  83 

Day  84 

Day  85 

Sixth  Average  

5.155 

5.149 

5.158 

5.153 

5.158 

Seventh  Average  

7.976 

11.707 

5.821 

6.290 

8.730 

HABIT  FORMATION  IN  ALBINO  RATS 


17 


TV 
Sixth  Average           ....... 

LBLE   Ila—  (Continue 

Day  86            Day  87 
5.158            5.158 

6.170          5.633 

Day  91            Day  92 

5.158          5.158 
7.170        10.730 

Day  96            Day  97 

5.158          5.158 
7.364          6.679 

Failed 
to  learn 
0 

d) 

Day  88            Day  89 
5.158            5.158 

6.364          5.947 

Day  93            Day  94 
5.158            5.158 

8.296          7.719 

Day  98            Day  99 

5.158          5.158 
7.736          7.604 

Days  required 
to  learn 
32.93 

44.00+ 

Seventh  Average     

Sixth  Average             

Seventh  Average  

Sixth  Average               .... 

Seventh  Average  

• 
Sixth  Average 

Seventh  Average. 

2 

Day  90 

5.158 
11.553 

Day  95 
5.158 

6.353 

Day  100 

5.158 
7.559 


TABLE    lib 
THE  MAZE 

AVERAGE  ABSOLUTE  RETENTION  OF  SIXTH  AND  SEVENTH  GENERATION  INBRED  RATS 

Absolute  Retention 
after  60  Days'  Rest 

Sixth  Average 65.443  seconds 

Seventh  Average 126 . 680  seconds 


TABLE   lie 
THE  MAZE 

DAILY  RELEARNING  AVERAGES  OF  SIXTH  AND  SEVENTH  GENERATION  INBRED  RATS 

(Time  in  seconds) 


Sixth  Average 

Seventh  Average. 


Sixth  Average. . . 
Seventh  Average. 


Sixth  Average. . . 
Seventh  Average. 


Sixth  Average. .. 
Seventh  Average. 


Sixth  Average . . . 
Seventh  Average . 


Sixth  Average 

Seventh  Average. , 


Day    1 

31.866 
45.352 

D*y    6 

8.174 
6.264 

Day  11 
6.163 

6.304 

Day  16 

5.628 
5.656 

Day  21 
6.186 

5.656 

Day  26 

6.349 
5.656 


Day    2 

10.357 
17.392 

Day    7 

7.426 
8.312 

Day  12 
6.054 

5.720 

Day  17 
5.674 

5.656 

Day  22 

5.897 
5.656 

Day  27 

5.711 
5.656 


Day    3 
11.043 

7.344 

Day    8 

6.351 
7.456 

Day  13 
5.886 

6.576 

Day  18 
5.689 

5.656 

Day  23 
5.911 

5.656 

Day  28 

6.006 
5.656 


Day    4 
9.009 

11.104 

Day    9 
6.111 

6.584 

Day  14 

5.660 
5.656 

Day  19 

6.163 
5.656 

Day  24 

6.206 
5.656 

Day  29 
5.909 

5.656 


Day    5 

8.071 
8.064 

Day  10 

6.129 
7.936 

Day  15 

5.563 
5.656 

Day  20 

5.740 
5.656 

Day  25 

5.811 
5.656 

Day  30 

5.874 
5.656 


18 


GARDNER  CHENEY  BASSET 


TV 

Sixth  Average  
Seventh  Average  

LBLE   He—  (Continue 

Day  31            Day  32 

5.989          5.994 
5.656          5.656 

Day  36            Day  37 
6.014             6.063 

5.656          5.656 

Day  41            Day  42 

5.657          5.917 
5.656          5.656 

Day  46            Day  47 

6.166          5.871 
5.656          5.656 

Failed 
to  Relearn 
2 

d) 

Day  33            Day  34 

5.634          5.914 
5.656          5.656 

Day  38            Day  39 

5.991          5.806 
5.656          5.656 

Day  43            Day  44 

5.823          5.777 
5.656          5.656 

Day  48       '   ,Day  49 
6.014             5.800 

5.656          5.656 

Days  Required 
to  Relearn 
14.14  + 
8.60 

Day  35 
6.040 

5.656 

Day  40 
5.751 

5.656 

Day  45 
5.934 

5.656 

Day  50 
5.711 

5.656 

Sixth  Average  

Seventh  Average 

Sixth  Average.  .,  
Seventh  Average  

Sixth  Average 

Seventh  Average  
Sixth  Average  . 

Seventh  Average  . 

0 

TABLE    lid 
THE  MAZE 
ANATOMICAL  DATA  OF  SIXTH  AND  SEVENTH  GENERATION  INBRED  RATS 


Sixth  Average 

Body 
Length 
in  mm. 
200  71 

Body            Brain             Cord 
Weight         Weight         Weight 
in  grms.        in  grms.        in  grms. 
195  04          1  75234          53881 

Water 
in   Brain 
per  cent 
78  49 

Seventh  Average.  .  . 
Sixth  Average 

....   184.71 

Water 
in  Cord 
per 
cent 
,.     71.73 

152.47          1.63286         .50794 

Per  cent                 Per  cent 
Brain  Weight        Brain  Weight 
in  Relation  to        in  Relation  to 
Body  Length        Body  Weight 
.87418                      .91653 

78.51 

Age 
killed 
Days 

196 

Seventh  Average 

71.70 

.88219                    1.07851 

207 

.  In  Plate  IV  is  shown  the  curve  of  learning  (below)  and  of 
relearning  (above)  of  the  6th  generation  of  inbred  rats  compared 
with  those  of  the  7th.  These  curves  are  constructed  from  figures 
given  in  Table  II.  The  curve  of  the  6th  generation  rats  is  indi- 
cated by  the  broken  line,  that  of  the  7th  generation  by  the  solid 
line.  The  ordinates  show  the  average  daily  time  in  seconds  for 
each  group,  and  the  abscissae  the  number  of  the  day  in  which 
such  time  was  made.  From  the  twenty-second  day  the  curve 
of  learning  of  the  6th  generation  lies  below  the  six-second  mark, 
and  from  the  eighty-third  day  is  flat  at  5.158  seconds,  signi- 
fying that  on  that  day  the  last  of  this  group  had  perfected  the 
habit.  The  7th  generation  learning  curve  is  very  irregular 


HABIT  FORMATION  IN  ALBINO  RATS 


19 


throughout  its  length  and  never  approaches  the  appearance  of 
perfect  learning.  The  7th  generation  relearning  curve,  however, 
is  slightly  better  than  that  of  the  6th,  being  flat  from  the  four- 
teenth day  at  5.656  seconds.  But  it  is  again  necessary  to  call 
attention  to  the  fact  that  this  was  a  selected  group,  the  two 


Plate  IF, 
The 


7—  S«n.    ln>«d 


au-  fctt5.n--nH5«t, 

>>    Siti.tiii  sii.mi 


R.Icatrmnj). 


rats  failing  to  learn  having  been  thrown  out  and  not  tested  for 
relearning. 

The  similarity  in  behavior  of  the  rats  of  the  control  series 
containing  blood  of  the  B  strain  (of  which  the  original  parents 
were  purchased  from  a  Baltimore  dealer)  to  the  behavior  of  the 
inbreds  has  already  been  mentioned.  The  length  of  time  re- 


20  GARDNER  CHENEY  BASSET 

quired  by  them  to  learn  the  maze  had  led  the  investigator  to 
suspect  a  less  than  normal  brain  weight;  and,  when  the  brains 
were  weighed,  this  was  found  to  be  the  case.  Table  III  presents 
a  comparative  summary  consisting  of  the  daily  averages  of  the 
nine  rats  containing  B  blood  and  of  the  twelve  control  rats 
lacking  it.  Eight  of  the  rats  containing  B  are  one-half  C  and 
one-half  B;  the  remaining  rat  is  one-half  C,  one-fourth  E,  and 
one-fourth  B.  That  the  C'  blood  is  not  a  factor  in  their  erratic 
behavior  is  proven  by  the  fact  that  most  of  the  rats  of  the  co- 
trol  series  not  containing  B  blood  do  also  contain  C.  In  order 
to  compare  the  behavior  of  control  rats  having  B  and  those 
lacking  it  with  that  of  the  inbred  rats,  cross  reference  may  be 
made  from  Table  III  to  the  inbred  averages  of  Table  I.  The 
control  rats  having  B  blood  shall  be  referred  to  in  Table  III 
as  Control  +B;  those  lacking  B  blood  as  Control  — B. 

The  tables  (I  and  III)  show  that  two  of  the  inbreds  and  one 
of  the  +B  failed  to  learn  the  maze;  the  — B  controls  had  all 
learned  at  the  end  of  the  twenty-fifth  day.  The  inbred  rats 
required,  on  the  average,  36.62-f-  days  to  learn;  the  -f-B  35.67  + 
days,  and  the  — B  but  16.42  days.  The  absolute  retention  of 
the  inbreds  was,  on  the  average,  81.558  seconds;  of  the  +B, 
72.475  seconds;  and  of  the  — B,  but  51.083  seconds.  Two  of 
the  inbreds  failed  to  relearn;  all  the  +  B  had  relearned  at  the 
end  of  the  twenty-second  day;  while  all  the  — B  had  relearned 
at  the  end  of  the  eighth  day.  The  inbreds  required,  on  the 
average,  12.68+  days  to  relearn;  the  +B,  8.24  days;  the  — B, 
but  4.08  days. 

In  these  criteria  of  ability  to  learn  the  maze,  the  inbred  rats 
did  the  least  well;  the  +B  rats  were,  in  each  instance,  above, 
but  not  far  from,  the  record  of  the  inbreds;  the  — B  were  much 
superior  to  either. 

Both  body  length  and  body  weight  were  greatest  m  the  in- 
breds, next  in  the  +B,  and  least  in  the  — B.  Actual  brain 
weight  was  least  in  the  inbreds,  much  greater  in  the  +B,  and 
slightly  greater  in  the  — B  than  in  the  +B.  The  relative  brain 
weight  (in  reference  to  body  length)  of  the  inbreds  was  5.46% 
less  than  that  of  the  — B;  that  of  the  +B  was  2.53%  less  than 
that  of  the  — B.  The  relative  brain  weight  (in  reference  to  body 
weight)  of  the  inbred  rats  was  10.02%  less  than  that  of  the  — B; 
that  of  the  +B  was  5.15%  less  than  that  of  the  — B.  As  might 


HABIT  FORMATION  IN  ALBINO  RATS 


21 


be  expected,  from  our  hypothesis  and  the  behavior,  the  average 
relative  brain  weight  of  the  +B>  rats  lies  between  that  of  the 
inbreds  and  of  the  — B. 

The  results  obtained  from  the  supposedly  normal  B  rats 
reinforce  the  former  conclusion  that  a  lesser  relative  brain  weight 
is  accompanied  in  a  similar  degree  by  a  lesser  ability  'to  form 

habits. 

TABLE    Ilia 

THE  MAZE 

DAILY  LEARNING  AVERAGES  OF  +B  AND  — B  NORMAL  CONTROL  RATS 
(Time  in  seconds) 

Day    2  Day    3  Day    4  Day    5 

187.729    88.511    36.160   29.689 
52.997   27.857  .  15.085   22.557 


Day    1 

Control +B 849.458 

Control— B..  248.380 


Control  +B. 
Control— B. 


Control  +B 
Control— B, 


Control  +B. 
Control— B, 


Control  +B. 
Control— B 


Control  +B. 
Control— B. 


Control  +B 
Control— B 


Control  -t-B. 
Control— B. 


Control  +B. 
Control— B. 


Control  +B. 
Control— B. 

Control  +B. 
Control— B. 

Control  +B. 
Control— B. 


Day    6 

20.093 
15.320 

Day  11 

8.142 
6.652 

Day  16 
6.702 

6.675 

Day  21 

6.529 
4.956 

Day  26 
6.031 

4.908 

Day  31 

6.756 
4.908 

Day  36 

5.758 
4.908 

Day  41 
5.923 

4.908 

Day  46 
5.791 

4.908 

Day  51 

5.874 
4.908 

Day  56 

5.679 
4.908 


Day    7 

15.822 
11.550 

Day  12 
9.544 

6.393 

Day  17 
7.822 
5.382 

Day  22 
6.973 

4.948 

Day  27 
6.156 

4.908 

Day  32 

6.294 
4.908 

Day  37 

5.704 
4.908 

Day  42 
6.461 

4.908 

Day  47 
5.501 

4.908 

Day  52 
5.963 

4.908 

Day  57 

5.546 
4.908 


Day    8 
13.066 

11.223 

Day  13 

8.907 
6.190 

Day  18 
7.067 

5.025 

Day  23 

6-804 
4.888 

Day  28 

6.240 
4.908 

Day  33 

6.006 
4.908 

Day  38 

5.887 
4.908 

Day  43 
5.999 

4.908 

Day  48 

5.466 
4.908 

Day  53 
5.572 

4.908 

Day  58 

5.959 
4.908 


Day    9 

10.276 
14.063 

Day  14 

7.476 
6.475 

Day  19 
7.467 

5.265 

Day  24 
6.719 

4.892 

Day  29 

6.280 
4.908 

Day  34 
6.287 

4.908 

Day  39 

5.971 
4.908 

Day  44 
5.706 

4.908 

Day  49 

5.586 
4.908 

Day  54 
6.559 

4.908 

Day  59 

5.690 
4.908 


Day  10 
12.964 

7.110 

Day  15 

9.289 
5.768 

Day  20 
7.040 
4.959 

Day  25 

6.102 
4.908 

Day  30 
6.142 

4.908 

Day  35 

5.842 
4.908 

Day  40 
5.861 

4.908 

Day  45 

6.159 
4.908 

Day  50 

5.643 
4.908 

Day  55 

5.732 
4.908 

Day  60 

5.723 
4.908 


22 


GARDNER  CHENEY  BASSET 


Control  +B. 
Control— B. 


Day  66 

Day  67 

Control  +B  

5.928 

5.914 

Control  -^B  ,  

4.908 

4.908 

Day  71 

Day  72 

Control  +B..  

5.692 

5.519 

Control—  B  

4.908 

4.908 

Day  76 

Day  77 

Control  +B  

5.550 

5.794 

Control  —  B  

4.908 

4.908 

Day  81 

Day  82 

Control  +B  

5.746 

5.673 

Control—  B  

4.908 

4.908 

Day  86 

Day  87 

Control  +B  

5.794 

5.488 

Control—  B  

4.908 

4.908 

Day  91 

Day  92 

Control  +B  

5.723 

5.346 

Control—  B  

4.908 

4.908 

v 

Day  96 

Day  97 

Control  +B  

5.630 

5.470 

Control—  B  

4.908 

4.908 

Failed 

to  Learn 

Control  +B 

1 

Control  —  B 

0 

TABLE   Ilia— (Continued 

Day  61             Day  62             Day  63  Day  64  Day  65 

6.052          7.346          6.857  5.821  5.794 

4.908          4.908          4.908  4.908  4.908 

Day  68  Day  69  Day  70 

5.528  5.963  5.643 

4.908  4.908  4.908 

Day  73  Day  74  Day  75 

5.426  5.603  5.381 

4.908  4.908  4.908 

Day  78  Day  79-  Day  80 

5.519  5.457  6.106 

4.908  4.908  4.908 

Day  83  Day  84  Day  85 

5.617  5.608  5.497 

4.908  4.908  4.908 

Day  88  Day  89  Day  90 

5.546  5.479  5.479 

4.908  4.908  4.908 

Day  93  Day  94  Day  95 

5.452  5.612  5.510 

4.908  4.908  4.908 

Day  98  Day  99  Day  100 

5.399  5.559  5.626 

4.908  4.908  4.908 

Days  Required 
to  Learn 
35.67+ 
16.42 


TABLE    Illb 

THE  MAZE 
AVERAGE  ABSOLUTE  RETENTION  OF  +B  AND  — B  NORMAL  CONTROL  RATS 

Absolute  Retention 
After  60  Days'  Rest 

Control  +B 72.475  seconds 

Control  — B . .  51 . 083  seconds 


TABLE    IIIc 

THE  MAZE 

DAILY  RELEARNING  AVERAGES  OF  +B  AND  — B  NORMAL  CONTROL  RATS 


Control  +B. 
Control— B. 


Control  +B, 
Control— B. 


Day    1 

36.215 
23.480 

Day    6 

8.075 
6.410 


Day    2 

29.230 
11.767 

Day    7 
7.200 

5.307 


Day    3 

10.930 
8.597 

Day    8 
6.970 

5.223 


Day    4 

11.180 
5.873 

Day    9 
6.340 

5.223 


Day    5 

7.990 

5.587 

Day  10 
6.240 

5.223 


HABIT  FORMATION  IX  ALBINO  RATS 


23 


TABLE  IIIc—  (Continued) 

Day  11            Day  12            Day  13            Day  14 

Control  +B                                  5.935          5.750          5.740          5.700 
Control—  B     5.223          5.223          5.223          5.223 

Day  15 

5.835 
5.223 

Day  20 
5.765 
5.223 

Control  +B 

Day  16 

7.090 
5.223 

Day  21 
6.200 

5.223 

Day  17 

5.725 
5.223 

Day  22 
5.415 
5.223 

Failed 
to  Relearn 
0 
0 

Day  18            Day  19 

5.890          5.550 
5.223          5.223 

to    Day  50 

Days   Required 
to  Relearn 
8.24 
4.08 

Control  —  B                

Control  -fB  
Control—  B  

Control  +B 

Control—  B.  . 

Body            Brain            Cord 
Weight         Weight         Weight 
in  grms.        in  grms.        in  grms. 
175.73          1.75378         .5419'. 
168.18          1.75428         .51643 

Per  cent                   Per  cent 
Brain    Weight        Brain    Weight 
in  Relation  to        in  Relation  to 
Body  Length           Body  Weight 
.90406                    1.02303 
.92748                   1.07861 

Water 
in  Brain, 
per  cent 
78.25 
78.37 

Age 
killed, 
Days 

200 
175 

TABLE    Hid 

THE  MAZE 

ANATOMICAL  DATA  OF  +B  AND  — B  NORMAL  CONTROL  RATS 

Body 

Length 

in  mm. 

Control  +B 193.00 

Control— B 189.50 

Water 

in  Cord, 

Per 

cent 

Control +B 71.48 

Control— B 71.81 

In  Plate  V  is  shown  the  curve  of  learning  (below)  and  of 
relearning  (above)  of  the  inbred  and  +B  rats  compared  with 
those  of  the  — B.  The  inbred  curve  is  represented  by  the  solid 
line,  the  +B  by  the  heavy  broken  line,  and  the  — B  by  the 
lighter  broken  line.  The  ordinates  show  the  average  daily  time 
in  seconds  for  each  group,  and  the  abscissae  the  number  of  the 
day  in  which  such  time  was  made.  From  the  twentieth  day  the 
— B  curve  is  flat  at  4.9  seconds.  Neither  the  inbred  nor  the  +B 
curves  flatten  entirely,  although  the  -f  B  curve  of  learning  is 
more  regular  than  that  of  the  inbreds.  The  curve  of  relearning 
(lacking  the  two  inbreds  and  one  -f-B  that  failed  to  learn)  shows 
little  difference  between  the  three  groups.  But  even  here, 
although  the  inbred  and  +B  are  selected  groups,  the  — B  re- 
mains superior  to  both,  and  the  +B  is  slightly  superior  to  the 
inbred  rats. 


24 


GARDNER  CHENEY  BASSET 


-p  ^  -»  i  s 
£  «-  •  - 1 5 
P-  £  l«» 

P*       M   pQ   >i/ 


I1- 


HABIT  FORMATION  IN  ALBINO  RATS  25 

IV.    EXPERIMENT  2:    THE  PRELIMINARY  INCLINED  PLANE 

The  apparatus  used  in  this  experiment  (see  Plate  VI)  was 
designed  especially  to  make  a  problem  exceptionally  difficult  to 
learn,  and  in  this  purpose  it  exceeded  expectations.  The  basic 
principle  is  the  same  as  that  of  the  apparatus  designed  and  used 


Plate  1ZI.  The  Inclined  "Plant. 

by  Watson  in  his  experiments  at  the  University  "of  Chicago, 
called  by  him  the  "  Inclined  Plane,"  and  which  is  described  and 
illustrated  in  his  monograph  "Animal  Education,"  page  37.5 
But  my  apparatus  differs  from  his  in  several  respects. 

Plate  VI  shows  in  detail  the  construction  and  method  of 
operation.  The  food  box,  A,  is  framed  of  wood,  eleven  by 

5  Watson:  Animal  Education,  Chicago,  1903. 


26  GARDNER  CHENEY  BASSET 

twelv.e  inches  base,  eleven  inches  in  height,  and  is  covered  on 
top  and  sides  with  three-eighths  inch  heavy  wire  mesh.  It  is 
fitted  with  a  hard  rubber  door,  d,  three-sixteenths  inch  thick, 
five  inches  high,  and  four  and  one-fourth  inches  wide.  To  the 
inner  side  of  the  door  is  fastened  a  cord  which  passes  over  a 
pulley,  p,  and  is  weighted  at  the  other  end  with  a  piece  of  lead, 
1,  of  sufficient  weight  to  insure  the  opening  of  the  door  upon 
releasing  the  latch.  B  shows  the  device  for  latching  and  re- 
leasing the  door.  A  short  distance  above  the  door  is  fastened 
a  three-inch  electrical  magnet,  m;  directly  below  that  is  a  steel 
wire,  s.w.,  surmounted  by  a  steel  disk,  s.d.,  of  the  same  diameter 
as  the  core  of  the  magnet.  The  steel  wire  holds  the  door  by 
dropping  through  holes  in  two  brass  plates,  g,  which  serve  as 
guides,  to  a  point,  behind  another  brass  plate  which  is  set  at 
the  top  of  and  behind  the  door,  one  and  one-half  millimeters 
below  the  top.  The  setscrew,  s.s.,  placed  on  the  steel  wire  above 
the  lower  guide  prevents  any  further  drop.  When  the  steel  wire 
holds  the  door  the  disk  is  two  mm.  below  the  magnet ;  when 
the  disk  is  drtiwn  up  to  the  magnet  one-half  mm.  clearance  is 
allowed  for  the  door  to  swing  back.  Back  of  the  feeding  box, 
A,  is  placed  the  inclined  plane,  I. P. 

The  inclined  plane  has  a  hard  rubber  base  three-eighths  inch 
thick,  six  inches  long,  and  .two  and  three-eighths  inches  wide. 
Upon  pivot  standards  rising  from  the  middle  of  the  base  rests 
the  plane  itself.  The  plane  is  of  wood  fibre  and  of  the  same 
dimensions  as  the  base.  It  is  weighted  at  the  end  nearest  the 
feeding  box  in  order  to  insure  its  return  to  position  after  use. 
At  the  end  opposite  the  weight  and  farthest  from  the  feeding 
box,  platinum  electrical  contacts,  e.c.,  are  placed  in  both  base 
and  plane.  The  power  is  provided  through  wires  connecting 
the  regular  electric  lighting  system,  115  volts,  direct  current, 
with  the  wired  apparatus.  A  32  candle  power  lamp  is  placed 
in  the  series  in  order  to  avoid  any  danger  of  short-circuiting. 
To  make  the  contact  and  allow  the  current  to  pass  through 
the  magnet,  thus  raising  the  steel  wire  and  releasing  the  door, 
it  is  necessary  for  the  rat  to  step  on  the  point  of  operation,  o, 
which  lies  well  out  toward  the  end  of  the  plane.  On  account 
of  a  certain  amount  of  latency  in  the  operation  of  the  magnet, 
the  rat  must  not  only  make  the  contacts  touch,  but  must  also 
inhibit  further  action,  remaining  on  the  point  of  operation  until 


HABIT  FORMATION  IN  ALBINO  RATS  27 

click  of  the  disk  meeting  the  magnet  is  heard.  Over  the  food 
box  and  plane  is  placed  a  cage,  C,  constructed  of  one-half  inch 
heavy  wire  mesh,  the  base  measurements  of  which  are  twenty- 
four  by  twenty-four  inches  and  the  height  fourteen  inches.. 
This  allows  the  rat  ample  room  to  explore  all  sides  of  and  above 
the  food  box.  When  the  rat  is  placed  within,  the  entrance,  e, 
to  the  cage  is  closed. 

The  preliminary  inclined  plane  experiment  was  not  intended 
so  much  as  a  decisive  experiment  as  to  test  the  efficiency  of 
the  apparatus.  The  results,  however,  are  significant  and,  there- 
fore, included  here. 

The  object  of  this  experiment  was  to  have  each  rat  learn  to 
reach  the ,  interior  of  the  food  box  from  the  cage  entrance  in 
the  least  possible  period  of  time.  The  procedure  of  a  perfectly 
trained  rat  was  to  run  from  the  entrance,  e,  to  the  point  of 
operation,  o,  remaining  there  until  the  click  of  the  disk  against 
the  magnet  insured  the  door  being  open,  then  running  through 
the  door  of  the  box  to  the  food  which  was  placed  within  at  point 
f.  The  starting  time  was  taken  when  the  animal  entered  at  e, 
another  when  the  magnet  clicked,  and  the  final  time  when  the 
food  box  was  entered.  The  object  of  recording  the  two  periods 
of  time  was  that  it  had  been  anticipated  that  differences  in 
association  between  the  inbred  series  and  the  control  rats  might 
appear.  But,  as  in  both  series  the  association  was  practically 
perfect  by  the  third  day,  a  comparison  of  such  differences  was 
thought  useless. 

In  preparation  for  the  experiment  each  animal,  beginning  at 
-the  age  of  sixty-five  days,  was  fed  alone  in  the  food  box,  the 
door  remaining  open,  ten  minutes  daily  for  five  consecutive 
days.  This  gave  the  rat  an  opportunity  to  become  acquainted 
with  .all  parts  of  the  interior  of  both  box  and  cage,  and  also 
accustomed  him  to  a  reduced  feeding  time.  At  the  age  of  seventy 
days  the  experiment  began.  Six  males  and  five  females  from  the 
inbred  strain  were  used  and,  as  control,  an  equal  number  of 
males  and  females  from  the  normal  series.  Ail  the  inbred  rats 
were  from  the  6th  generation.  The  stimulus  used  was  their 
regular  food,  bread  soaked  in  milk. 

As  one  of  the  first  rats  used  consumed  fourteen  hours  before 
his  first  accidental  success,  it  was  decided  to  use  "cumulative 
time"  for  the  first  few  trials.  By  this  method  each  rat  was 


28  GARDNER  CHENEY  BASSET 

allowed  to  work  thirty  minutes  and  then,  if  unsuccessful,  he  was 
taken  out,  the  food  box  door  was  opened,  and  he  was  then  re- 
turned to  feed  for  five  minutes  and  used  no  more  that  day. 
When  they  began  to  succeed  within  the  half  hour,  each  rat  was 
required  to  open  and  enter  the  food  box  five  times  daily.  At 
the  end  of  the  fifth  trial  it  was  allowed  to  feed  for  five  minutes, 
but  was  permitted  no  more  food  until  the  completion  of  the 
next  day's  experiment.  Each  rat  was  used  daily  for-  twenty 
days,  making  one  hundred  trials.  As  a  time  limit  had  been 
placed,  no  criterion  of  perfect  learning  was  established  for  this 
experiment.  At  the  conclusion  of  the  learning  experiment  the 
rats  were  fed  in  the  runway,  which  has  already  been  described, 
for  sixty  days.  At  the  end  of  this  period  they  were  tested  for 
absolute  retention  .and  relearning,  and  were  worked  for  five 
days,  twenty-five  trials,  in  order  to  ascertain  the  effects  of  the 
previous  training. 

In  Table  IV  is  a  comparative  summary  consisting  of  the  daily 
averages  of  the  entire  inbred  group  and,  directly  beneath,  the 
corresponding  daily  averages  of  the  entire  normal  control  group. 

From  the  eleventh  day  the  daily  time  averages  of  the  control 
rats  are  less  than  those  of  the  inbreds.  The  absolute  retention 
of  the  control  rats  is  superior  to  that  of  the  inbreds.  In  the  five 
days  allotted  to  testing  the  effects  of  previous  training,  the  average 
time  of  the  control  rats  is  less  each  day  than  that  of  the  inbreds. 

In  these  criteria  of  ability  the  rats  of  the  normal  control  series 
are  shown  to  be,  on  the  average,  superior  to  those  of  the  inbred 
series. 

Body  length  of  the  inbred  rats  used  in  the  preliminary  inclined 
plane  is,  on  the  average,  slightly  greater  than  is  the  case  with  the 
control;  body  weight,  however,  is  a  trifle  less.  The  average 
actual  brain  weight  of  the  inbreds  is  less  than  that  of  the  control. 
The  relative  brain  weight  (in  reference  to  body  length)  of  the 
inbreds  is  11.61%  less  than  that  of  the  control.  The  relative 
brain  weight  (in  reference  to  body  weight)  of  the  inbreds  is  1 1.65% 
less  than  that  of  the  control.  Although  killed  at  a  later  age,  the 
percentage  of  water  in  brain  and  cord  of  the  inbreds  is  greater 
than  is  the  case  with  the  control. 

The  preliminary  inclined  plane  figures  presented  in  this  table 
(IV)  support  the  hypothesis  that  a  less  than  normal  average 
brain  weight  in  a  strain  of  rats  is  accompanied  by  a  lesser  ability 
to  form  habits. 


HABIT  FORMATION  IN  ALBINO  RATS 


29 


TABLE    IVa 

THE  PRELIMINARY  INCLINED  PLANE 

DAILY  LEARNING  AVERAGES  OF  INBRED  AND  NORMAL  CONTROL  RATS 
(Time  in  seconds) 


Inbred  Average 

Control  Average 


Inbred  Average 

Control  Average 


Inbred  Average . . 
Control  Average . 


Day    1 

1965.858 
2470.393 


Day  2 

1631 . 178 
971.102 


Day    3 

60.302 
79.775 


Day    4  Day    5 

45.916        28.116 
27.564        21.840 


Inbred  Average . . 
Control  Average . 


Day    6 
11.120 
20.305 

Day    7 
14.833 

10.375 

Day  11 

6.262 
5.342 

Day  12 
9.465 

5.015 

Day  16 

7.360 
5.062 

Day  17 

6.247 
3.727 

Day    8 

9.095 
9.869 

Day    9 
16.855 

8.971 

Day  10 
7.109 

8.058 

Day  13 
7.658 

5.055 

Day  14 
10.916 

4.425 

Day  15 
10.291 
4.513 

Day  18 

5.531 

4.800 

Day  19 
8.811 
5.815 

Day  20 
10.251 

5.622 

TABLE   IVb 

THE  PRELIMINARY  INCLINED  PLANE 
AVERAGE  ABSOLUTE  RETENTION  OF  INBRED  AND  NORMAL  CONTROL  RATS. 

Absolute    Retention 
After  60  Days'  Rest 

Inbred  Average 59.309  seconds 

Control  Average 49 . 164  seconds 

TABLE    IVc 

THE  PRELIMINARY  INCLINED  PLANE 
DAILY  RELEARNING  AVERAGES  OF  INBRED  AND  NORMAL  CONTROL  RATS 

(Time  in  seconds) 

Day    1  Day    2  Day    3  Day    4  Day    5 

Inbred  Average 24.302          9.905        11.516          8.149          7.869 

Control  Average 17.102          5.498          5.869          4.262          6.651 

TABLE   IVd 

THE  PRELIMINARY  INCLINED  PLANE 
ANATOMICAL  DATA  OF  INBRED  AND  NORMAL  CONTROL  RATS 

Body 
Length 
in  mm. 

Inbred  Average 190.82 

Control  Average 189 . 45 

Water 

in  Cord, 

Per 

cent 

Inbred  Average 71 .436 

Control  Average 71 . 128 


Body 
Weight 
in  grms. 
166.50 
168.08 

Brain 
Weight 
in  grms. 
1.62031 
1.81946 

Cord 
Weight 
in  grms. 
.47535 
.52819 

Water 
in  .tsrain, 
per  cent 
78.565 
77.982 

Per  cent 
Brain    Weight 
in  Relation  to 
Body  Length 
.84929 
.96084 

Per  cent 
Brain    Weight 
in  Relation  to 
Body  Weight 
.98140 
1.09571 

Age 
killed, 
Days 

194 

170 

30  GARDNER  CHENEY  BASSET 

In  Plate  VII  is  shown  the  curve  of  learning  (left)  and  of  re- 
learning  (right)  of  the  inbred  rats  compared  with  those  of  the 
normal  control.  These  curves  are  constructed  from  figures 
given  in  Table  IV.  The  curve  of  the  inbred  rats  is  indicated  by 
the  solid  line,  that  of  the  normal  control  by  the  broken  line. 
The  ordinates  give  the  average  daily  time  in  seconds  for  each 
group,  and  the  abscissae  the  number  of  the  day  in  which  such 
time  was  made.  The  time  required  by  both  inbred  and  control 
rats  for  the  first  four  days  was  so  long  that  it  is  represented  here 
by  figures  and  does  not  appear  in  the  curve.  Both  learning 
curves  are  irregular,  but  on  the  eleventh  day  that  of  the  control 
passes  permanently  below  that  of  the  inbred.  The  curves  of 
relearning  show  that  the  inbreds  had  failed  to  benefit  by  practice 
to  so  great  an  extent  as  the  normal  control. 

V.     EXPERIMENT  3:    THE   INCLINED  PLANE 

The  apparatus  used  in  this  experiment  was  the  same  as  that 
used  in  Experiment  2 :  the  Preliminary  Inclined  Plane.  The 
animals  were  prepared  in  the  same  way  as  for  the  previous 
experiment,  and  began  work  at  the  age  of  seventy  days.  Sixteen 
males  and  fourteen  females  from  the  inbred  strain  were  used  and, 
as  control,  an  equal  number  of  males  and  females  from  the  normal 
series.  Of  the  inbred  rats,  fifteen  were  from  the  seventh  genera- 
tion, fourteen  from  the  eighth,  and  one  from  the  ninth.  As  the 
behavior  of  the  single  ninth  generation  rat  did  not  vary  greatly 
from -the  average  of  the  eighth  generation,  her  results  have  been 
included  in  the  tables  and  curves  of  the  eighth  generation.  The 
stimulus  used  in  this  experiment  was  the  same  as  in  the  two 
preceding,  bread  soaked  in  milk. 

Cumulative  time  was  used  in  recording  the  earlier  trials  as  in  the 
previous  experiment.  When  the  rats  began  to  succeed  in  entering 
the  food  box  within  the  half  hour,  each  one  was  required  to  open 
and  enter  the  food  box  three  times  each  day.  At  the  end  of  the 
third  trial  it  was  allowed  to  feed  in  the  box  for  five  minutes,  but 
was  permitted  no  more  food  until  the  completion  of  the  next 
day's  experiment.  Each  rat  was  used  daily  until  it  had  learned 
the  problem  perfectly,  the  criterion  of  perfection  being  three 
perfect  trials  for  each  of  three  successive  days.  A  perfect  trial 
consisted  in  running  frbm  the  entrance  to  the  point  of  operation 
on  the  plane  at  the  rear  of  the  food  box,  opening  the  door,  run- 


HABIT  FORMATION  IN  ALBINO  RATS 


31 


V       O 

43     O 

to 


32  GARDNER  CHENEY  BASSET 

ning  around  and  entering  the  box,  all  within  four  seconds;  but, 
if  the  time  consumed  in  opening  the  box  after  passing  the  entrance 
was  more  than  two  seconds,  or  if  the  time  consumed  in  entering 
the  box  after  having  opened  the  door  was  more  than  two  seconds, 
the  trial  was  considered  a  failure.  Thus  it  was  possible  for  a  rat 
to  have  a  perfect  trial  in  as  long  a  total  time  as  four  seconds,  or  a 
failure  in  a  less  total  time.  Those  rats  failing  to  learn  within  one 
hundred  days  (three  hundred  trials)  were  no  longer  used  for 
experimentation.  Those  rats  learning  the  inclined  plane  were,  at 
the  conclusion  of  the  experiment,  fed  for  sixty  days  in  the  runway. 
At  the  end  of  this  period  they  were  tested  for  absolute  retention 
and  relearning. 

Three  of  the  rats  formed  the  habit  of  lifting  the  plane  at  the 
end  nearest  the  food  box  and  thus  formed  the  contact,  but  this 
method  apparently  affected  neither  the  rapidity  of  each  trial 
nor  the  number  of  days  required  for  perfect  learning.  One  of  the 
normal  rats  placed  his  nose  between  the  electrical  contacts  and 
received  a  shock,  but  other  than  one  squeal  and  a  vigorous 
rubbing  of  the  nose,  he  showed  no  evidence  of  harm  and  had 
apparently  forgotten  the  experience  the  following  day.  Some 
of  the  rats  jumped  to  the  point  of  operation  from  a  distance; 
some  placed  the  fore  paws  on  the  end  of  the  plane  and  pressed 
down;  and  still  others  ran  slowly  around  to  the  plane,  halting 
an  instant  on  the  point  of  operation,  and  then  continued  the  run 
around  to  the  door.  As  a  rule,  the  last  made  the  best  time.  As 
in  the  maze  experiment,  many  of  the  inbred  rats  were  subject  to 
errors  which  persisted  throughout  the  experiment.  In  particular 
may  be  mentioned  one  rat  that  invariably  formed  a  loop  in  the 
course  from  the  entrance  to  the  point  of  operation. 

The  shortest  period  of  time  required  by  an  inbred  rat  to  learn 
the  inclined  plane  perfectly  was  twelve  days ;  by  a  normal  con- 
trol rat,  nine  days.  Eleven  inbred  rats  and  one  control  failed 
to  learn  the  inclined  plane  within  the  one  hundred  days  allowed. 

In  Table  V  is  presented  a  comparative  summary  consisting  of 
the  daily  averages  of  the  entire  inbred  group  and,  directly 
beneath,  the  corresponding  daily  averages  of  the  entire  normal 
control  group.  The  inbred  rats  required,  on  the  average,  73.70  + 
days  to  learn  the  inclined  plane;  the  controls  but  45. 9 74- 
day  s.  The  absolute  retention  of  the  inbreds  was,  on  the  aver- 
age, 31.842  seconds;  of  the  controls,  but  22.587  seconds.  All 


HABIT  FORMATION  IN  ALBINO  RATS 


33 


the  inbreds  had  relearned  at  the  end  of  the  twenty-fourth  day; 
but  all  the  controls  had  relearned  at  the  end  of  the  seventeenth 
day.  The  inbred  rats  required,  on  the  average,  6.74  days  to  re- 
learn;  the  controls  but  4.68  days. 

In  all  these  criteria  of  ability,  learning,  absolute  retention  and 
relearning,  the  rats  of  the  normal  control  series  are  shown,  on 
the  average,  to  be  superior  to  those  of  the  inbred  series. 

The  body  length  of  the  inbred  rats  used  in  the  inclined  plane 
experiment  is,  on  the  average,  a  trifle  greater  than  that  of  the 
controls;  the  body  weight  is  slightly  less.  The  average  actual 
brain  weight  of  the  inbreds  is  less  than  that  of  the  controls.  The 
relative  brain  weight  (in  reference  to  body  length)  of  the  inbreds 
is  5.89%  less  than  that  of  the  controls.  The  relative  brain  weight 
(in  reference  to  body  weight)  of  the  inbreds  is  2.38%  less  than  that 
of  the  controls.  Although  the  inbred  rats  were  killed,  on  the 
average,  at  a  more  advanced  age  than  the  normal  controls,  the 
percentage  of  water  in  brain  and  cord  is  higher. 

The  figures  presented  in  Table  V  support  the  hypothesis  that  a 
less  than  normal  average  brain  weight  in  a  strain  of  rats  is  ac- 
companied by  an  average  lesser  ability  to  form  habits. 


TABLE  Va 
THE  INCLINED  PLANE 
DAILY  LEARNING  AVERAGES  OF  INBRED  AND  NORMAL  CONTROL  RATS 


Inbred  Average . . 
Control  Average. 


Inbred  Average 

Control  Average 


Inbred  Average . . 
Control  Average . 


Inbred  Average 

Control  Average 


Inbred  Average . 
Control  Average. 


Inbred  Average . 
Control  Average. 


(Time 

Day    1 

4673.131 
2769.953 

in  seconds) 

Day    2 

1218.976 
1072.722 

Day    3 

166.997 
133.287 

Day    4 

56.576 
61.600 

Day    5 

22.926 
23.995 

Day    6 
36.878 

25.874 

Day    7 

12.422 
13.478 

Day    8 
11.061 

11.704 

Day    9 

10.751 
11.280 

Day  10 

8.136 
6.961 

Day  11 
9.383 

6.759 

Day  12 

7.876 
6.858 

Day  13 
8.625 

6.347 

Day  14 
7.188 

7.045 

Day  15 
9.586 

6.383 

Day  16 

8.710 
5.069 

Day  17 
8.069 

5.400 

Day  18 

7.364 
6.158 

Day  19 
9.191 

5.376 

Day  20 
6.717 
5.352 

Day  21 

6.919 
5.284 

Day  22 

6.363 
4.378 

Day  23 

6.951 
5.173 

Day  24 
6.458 

5.280 

Day  25 

7.329 
5.025 

Day  26 
5.674 

4.978 

Day  27 

6.262 
5.139 

Day  28 
6.627 

5.276 

Day  29 

5.514 
4.302 

Day  30 

27.802 
4.303 

34 


GARDNER  CHENEY  BASSET 


T 

Inbred  Average  
Control  Average  

'ABLE  Va—  (Continue 

Day  31            Day  32 

7.440          6.707 
4.354          5.075 

Day  36            Day  37 

'6.957          5.334 

4.121          4.457 

Day  41            Day  42 

4.898          4.938 
3.748          4.033 

Day  46            Day  47 

4.011          5.076 
3.367          3.091 

Day  51             Day  52 

4.762          4.408 
3.044          3.160 

Day  56            Day  57 

4.072          3.916 
3.000          3.392     . 

Day  61            Day  62 

4.172          5.026 
3.173          3.251 

Day  66            Day  67 

4.160          3.955 
3.098          3.109 

Day  71            Day  72 

4.383          3.869 
2.976          3.072 

Day  76            Day  77 

3.726          3.669 
2.667          2.799 

Day  81             Day  82 

3.359          3.465 
3.094          2.663 

Day  86            Day  87 

3.729          3.388 
2.763          2.834 

Day  91             Day  92 

3.501          3.393 
2.683          2.665 

Day  96            Day  97 

2.999          3.460 
2.772          2.657 

Failed 
to  Learn 
11 

4) 

Day  33            Day  34 

6.416          6.775 
3.583          3.868 

Day  38            Day  39 

5.689          5.479 
3.958          4.905 

Day  43            Day  44 

5.093          4.762 
3.446          3.729 

Day  48            Day  49 

3.831          4.991 
3.159          3.050 

Day  53            Day  54 

4.693          5.006 
2.841          2.924 

Day  58            Day  59 

5.909          6.235 
3.047         ,2.991 

Day  63            Day  64 

4.437          3.317 
2.848          3.951 

Day  68            Day  69 

5.858          4.806 
3.155          3.138 

Day  73            Day  74 
3.461             3.713 

3.163          2.640 

Day  78            Day  79 

3.646          4.043 
2.770          2.750 

Day  83            Day  84 

3.558          3.322 
2.665          2.652 

Day  88            Day  89 

3.686          3.639 
2.669          2.681 

Day  93            Day  94 

4.124          3.463 
2.623          2.732 

Day  98            Day  99 

3.604          2.982 
2.608          2.946 

Days  Required 
to  Learn 
73.70  + 
45.97+ 

Day35 

6.957 
4.024 

Day  40 
5.289 

4.096 

Day  45 
4.553 

3.857 

Day  50 

5.105 
3.113 

Day  55 
4.191 
3.759 

Day  60 

4.953 
3.375 

Day  65 

3.741 
3.035 

Day  70 
4.260 

2.949 

Day  75 

3.649 
3.129 

Day  80 
3.648 

2.839 

Day  85 

3.471 
2.823 

Day  90 
4.170 

2.663 

Day  95 

3.457 
2.846 

Day  100 
3.510 

2.637 

Inbred  Average  
Control  Average  

Inbred  Average 

Control  Average      

Inbred  Average 

Control  Average 

Inbred  Average        

Control  Average  

Inbred  Average  
Control  Average  

Inbred  Average  
Control  Average  

Inbred  Average      

Control  Average  

Inbred  Average 

Control  Average  

Inbred  Average 

Control  Average  
Inbred  Average  

Control  Average  

Inbred  Average  .  ,  

Control  Average  
Inbred  Average 

Control  Average  
Inbred  Average 

Control  Average 

Inbred  Average. 
Control  Average. 

2 

HABIT  FORMATION  IN  ALBINO  RATS 


35 


TABLE  Vb 
THE  INCLINED  PLANE 
AVERAGE  ABSOLUTE  RETENTION  OF  INBRED  AND  NORMAL  CONTROL  RATS 

Absolute  Retention 
After  60  Days'  Rest 

Inbred  Average 31 . 842  seconds 

Control  Average 22.587  seconds 


TABLE  Vc 

THE  INCLINED  PLANE 

DAILY  RELEARNING  AVERAGES  OF  INBRED  AND  NORMAL  CONTROL  RATS 

(Time  in  seconds) 


Inbred  Average . . 
Control  Average . 


Inbred  Average . . 
Control  Average . 


Inbred  Average . . 
Control  Average. 

Inbred  Average . . 
Control  Average. 


Inbred  Average . 
Control  Average . 


Day    1 

41.789 
22.598 

Day    2 
7.301 
6.198 

Day    3 

5.436 
4.279 

Day  4 
4.783 

3.985 

Day    6 
5.175 

3.057 

Day    7 
4.239 

3.569 

Day    8 

3.404 
3.598 

Day  9 

3.186 
3.021 

Day  11 

3.508 
2.929 

Day  12 

2.712 
3.676 

Day  13 

2.796 
3.200 

Day  14 

2.845 
2.633 

Day  16 

2.610 
2.776 

Day  17 

2.603 
2.586 

Day  18 

2.596 
2.586 

Day  19 

2.733 
2.586 

Day  21  Day  22 


2.607 

2.586 


Inbred  Average. . 
Control  Average . 


2.729 
2.586 

Failed 

to  Relearn 

0 

0 


Day  23 
2.596 

2.586 


Day  24 

2.554 
2.586 


Days  Required 

to  Relearn 

6.74 

4.68 


Day    5 

5.067 
5.021 

Day  10 
2.828 

3.293 

Day  15 

2.807 
2.664 

Day  20 

2.677 
2.586 

Day  25 

to  50 

2.554 
2.586 


TABLE  Vd 
THE  INCLINED  PLANE 


ANATOMICAL  DATA  OF  INBRED  AND  NORMAL  CONTROL  RATS 

Body 
Weight 
in  grms. 
184.37 
189.18 


Body 
Length 
in  mm. 

Inbred  Average 195 . 93 

Control  Average 194 . 43 


Brain 
Weight 
in  grms. 
1.72083 
1.81840 

Cord 
Weight 
in  grms. 
.53787 
.53922 

Water 
in  Brain 
per  cent, 
78.363 
78.319 

Water 

in  Cord, 

per 

cent 

Inbred  Average 71 .437 

Control  Average 71.223 


Per  cent 
Brain    Weight 
in  Relation  to 
Body  Length 
.87972 
.93474 

Per  cent 
Brain    Weight 
in  Relation  to 
Body  Weight 
.97889 
1.00275 

Age 
killed, 
Days 

220 
194 

36  GARDNER  CHENEY  BASSET 

In  Plate  VIII  is  shown  the  curve  of  learning  (below)  and  of 
relearning  (above)  of  the  inbred  rats  compared  with  those  of  the 
normal  control.  These  curves  are  constructed  from  figures 
given  in  Table  V.  The  curve  of  the  inbred  rats  is  indicated 
by  the  solid  line,  that  of  the  normal  control  by  the  broken 
line.  The  ordinates  give  the  average  daily  time  in  seconds 
for  each  group,  and  the  abscissae  the  number  of  the  day  in  which 
such  time  was  made.  As  in  the  other  learning  curves,  the 
time  required  by  both  inbred  and  control  rats  for  the  first 
four  days  was  so  long  that  it  is  represented  here  by  figures  and 
does  not  appear  in  the  curve.  The  descent  in  time  of  both 
inbred  and  control  rats  for  the  first  ten  days  is  quite  rapid, 
although  both  show  retardation  on  the  sixth  day.  From  the 
forty-first  day  the  curve  of  the  controls  lies  entirely  below  the 
four  second  mark.  The  inbred  curve,  throughout,  shows  great 
irregularities,  especially  on  the  thirtieth  day,  when  it  rises  to  an 
average  of  nearly  twenty-eight  seconds.  The  inbred  curve  of 
relearning  is  very  similar  to  that  of  the  control,  and  from  the 
twenty-third  day  coincides  with  it.  But  'again,  in  relearning,  we 
are  dealing  with  selected  groups,  the  eleven  inbreds  and  two 
controls  that  failed  to  learn  not  being  included.  The  inbreds  of 
this  selected  group  had  all  relearned  at  the  end  of  the  twenty- 
fourth  day;  the  control  at  the  end  of  the  seventeenth  day. 

In  Plate  IX  may  be  seen  the  distribution  curves  of  learning  of 
both  the  inbred  and  control  series  for  the  inclined  plane  experi- 
ment. The  time  is  given  in  days — in  groups  of  five  for  learning, 
singly  for  relearning.  It  is  very  apparent  that  the  advantage 
lies  wholly  in  favor  of  the  normal  control  series. 

Of  the  inbred  rats  used  in  the  inclined  plane  experiment, 
fifteen  were  from  the  seventh  generation,  fourteen  from  the 
eighth,  and  one  from  the  ninth.  In  Table  VI  is  presented  a 
comparative  summary  consisting  of  the  daily  averages  of  the 
seventh  and  eighth  generation  rats  used  in  the  inclined  plane 
experiment.  With  the  rats  of  the  eighth  generation  may  be 
included  the  one  from  the  ninth,  as  her  record  was  not  far  from 
the  average  of  the  eighth.  The  table  shows  that  four  of  the 
seventh  generation  and  seven  of  the  eighth  generation  failed  to 
learn  the  inclined  plane.  The  seventh  generation  required,  on 
the  average,  59.60+  days  to  learn;  the  eighth  generation, 
86.53+  days.  The  absolute  retention  of  the  seventh  genera- 


HABIT  FORMATION  IN  ALBINO  RATS 


37 


tion  was,  on  the  average,  44.945  seconds;  of  the  eighth'genera- 
tion,  13.825  seconds.  All  the  seventh  generation  had  relearned 
at  the  end  of  the  twenty-fourth  day;  but  all  the  eighth  genera- 
tion had  relearned  at  the  end  of  the  eighth  day.  The  seventh 
generation  required,  on  the  average,  8.00  days  to  relearn;  the 
eighth  generation  but  5.00  days. 


Vla.it  Effi. 
The  Inclined  Pi ane, 

Ittlrr.dStra.ia        

Mot  mal  Control     


Da«<  -    lifted    -  Ho^tnat 

IJ          1kl3:l3l  3.7 kl.  If 3 
3.                ILIt.m 

i  /**.y?7 


In  these  criteria  of  ability  the  seventh  generation  excelled  in 
learning,  the  eighth  in  absolute  retention  and  relearning.  But, 
again,  in  absolute  retention  and  relearning,  we  are  dealing  with 
selected  groups  as  the  seven  eighth  generation  and  four  seventh 
generation  rats  that  failed  to  learn  were  not  used.  There  seems, 
on  the  whole,  to  be  but  little  difference  between  the  abilities  of 


38 


GARDNER  CHENEY  BASSET 


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HABIT  FORMATION  IN  ALBINO  RATS 


39 


the   seventh   and   eighth    generations   except   that    the   former 
excelled  in  learning. 

The  body  length  and  body  weight  of  the  seventh  generation 
average  greater  than  those  of  the  eighth.  The  relative  brain 
weight  (in  reference  to  body  length)  of  the  seventh  generation  is 
5.20%  less  than  that  of  the  eighth.  The  relative  brain  weight 
(in  reference  to  body  weight)  of  the  seventh  generation  is  13.93% 
less  than  that  of  the  eighth.  The  actual  brain  weight  of  the 
seventh  generation,  however,  is  greater  than  that  of  the  eighth. 
The  percentage  of  water  in  brain  and  cord  of  the  seventh  generation 
is  greater  than  in  the  eighth. 


TABLE  VI 
THE  INCLINED  PLANE 

DAILY  LEARNING  AVERAGES  OF  SEVENTH  AND  EIGHTH  GENERATION  INBRED  RATS 

(Time  in  seconds) 


Day    1 

Day    2 

Day    3 

Day    4 

Day    5 

Seventh  Average  .  . 

...     5656.546 

1463.707 

123.213 

53.583 

17.159 

Eighth  Average  .  .  . 

3689.716 

974.245 

210.781 

58.369 

28.693 

Day    6 

Day    7 

Day    8 

Day    9 

Day  10 

Seventh  Average  .  . 

11.142 

11.373 

8.160 

8.845 

5.853 

Eighth  Average 

62.613 

13.471 

13.961 

12.657 

10.419 

Day  11 

Day  12 

Day  13 

Day  14 

Dav  15 

Seventh  Average  .  . 

10.855 

5.459 

6.037 

5.197 

6.367 

Eighth  Average  .  . 

7.911 

10.294 

11.213 

9.178 

12.805 

Day  16 

Day  17 

Day  18 

Day  19 

Day  20 

Seventh  Average.  . 

5.821 

4.732 

6.714 

6.351 

5.310 

Eighth  Average  .  .  . 

11.599 

11.407 

8.013 

12.030 

8.124 

Day  21 

Day  22 

Day  23 

Day  24 

Day  25 

Seventh  Average.  . 

5.592 

5.538 

4.934 

6.116 

5.481 

Eighth  Average  .  .  . 

8,245 

7.187 

8.969 

6.801 

9.177 

Day  26 

Day  27 

Day  28 

Day  29 

Day  30 

Seventh  Average.  . 

6.204 

5.636 

5.809 

»    3.965 

4.875 

Eighth  Average 

5.143 

6.889 

7.445 

7.063 

50.729 

5 

Day  31 

Day  32 

Day  33 

Day  34 

Day3 

Seventh  Average  .  . 
Eighth  Average.  .  .  , 

4.085 
10.795 

5.884 
7.529 

4.733 
8.099 

4.195 
9.355 

4.526 
9.388 

Day  36 

Day  37 

Day  38 

Day  39 

Day  40 

Seventh  Average  .  . 
Eighth  Average  .  .  . 

4.481 
9.433 

3.921 

6.747 

4.192 

7.186 

4.467 
6.491 

4.561 
6.017 

Day  41 

Day  42 

Day  43 

Day  44 

Day  45 

Seventh  Average  .  . 
Eighth  Average  . 

4.667 
5.130 

4.462 
5.413 

4.396 
5.791 

4.338 

5.187 

3.734 

5.373 

40 


GARDNER  CHENEY  BASSET 


T, 
Seventh  Average  

<\BLE  VI—  (Continue 

Day  46            Day  47 

3.435          4.121 
4.587          6.031 

Day  51             Day  52 

4.289          3.591 
5.235          5.226 

Day  56            Day  57 

3.251          3.584 
4.893          4.247 

Day  61             Day  62 

4.295          5.753 
4.049          4.299 

Day  66            Day  67 

3.331          3.571 
4.988          4.339 

Day  71             Day  72 

4.415          3.717 
4.350          4.021 

Day  76            Day  77 
3.760             3.601 

3.691          3.736 

Day  81             Day  82 

3.319          3.039 
3.398          3.891 

Day  86            Day  87 

3.251          3.037 
4.207          3.739 

Day  91            Day  92 

3.211          3.157 
3.792          3.629 

Day  96            Day  97 

2.725          2.650 
3.273          4.270 

Failed 
to  Learn 
4 

d 

Day  48            Day  49 

3.636          3.867 
4.027          6.116 

Day  53            Day  54 

4.219          4.969 
5.168          5.044 

Day  58            Day  59 

4.406          7.917 
7.412          4.553 

Day  63            Day  64 
4.731             3.006 

4.143          3.627 

Day  68            Day  69 

4.317          5.175 
7.398          4.437 

Day  73            Day  74 

3.388          3.233 
3.533          4.193 

Day  78            Day  79 
4.130             4.705 

3.162          3.381 

Day  83            Day  84 

3.322          3.135 
3.794          3.509 

Day  88            Day  89 

3.144          3.361 
4.228          3.916 

Day  93            Day  94 

3.273          2.913 
4.975          4.014 

Day  98            Day  99 

3.085          3.201 
4.123          2.763 

Days  Required 
to  Learn 
59.60  + 
86.53  + 

Day  EO 

4.277 
5.933 

Day  55 

3.627 

4.755 

Day  60 

4.325 
5.581 

Day  65 

3.331 
4.151 

Day  70 
4.565 

3.954 

Day  75 

3.620 
3.678 

Day  80 

3.623 
3.673 

Day  85 

3.424 
3.519 

Day  90 
3.837 

4.503 

Day  95 

2.678 
4.237 

Day  100 

3.067 
3.954 

Eighth  Average  

Seventh  Average  

Eighth  Average  

Seventh  Average  

Eighth  Average  
Seventh  Average  

Eighth  Average 

Seventh  Average  
Eighth  Average  

Seventh  Average  
Eighth  Average 

Seventh  Average  
Eighth  Average 

Seventh  Average  

Eighth  Average  

Seventh  Average  
Eighth  Average  

Seventh  Average  

Eighth  Average  

Seventh  Average  .  .    . 

Eighth  Average    

Seventh  Average. 

Eighth  Average  .  . 

7 

TABLE    VIb 
THE  INCLINED  PLANE 

AVERAGE  ABSOLUTE  RETENTION  OF  SEVENTH  AND  EIGHTH  GENERATION  INBRED 

RATS 

Absolute  Retention 
After  60  Days'  Rest 

*  Seventh  Average 44 .945  seconds 

Eighth  Average 13 . 825  seconds 


HABIT  FORMATION  IN  ALBINO  RATS 


41 


TABLE    Vic 

THE  INCLINED  PLANE 

DAILY  RELEARNING  AVERAGES  OF  SEVENTH  AND  EIGHTH  GENERATION  INBRED  RATS 


Seventh  Average. 
Eighth  Average. . 


Seventh  Average'. 
Eighth  Average. . 


Seventh  Average. 
Eighth  Average . . 


Seventh  Average. 
Eighth  Average . . 


Seventh  Average . 
Eighth  Average . . 


(Time  in  seconds) 

Day    1  Day    2 

66.322    9.265 
8.058    4.438 


Day    6 
6.297 

3.633 

Day  11 

4.285 
2.441 

Day  16 

2.733 

2.441 

Day  21 

2.727 
2.441 


Seventh  Average. . . 
Eighth  Average .... 


Day    7 

4.467 
3.925 

Day  12 

2.909 

2.441 

Day  17 
2.721 

2.441 

Day  22 

2.939 
2.441 

Failed 

to  Relearn 

0 

0 


Day    3 

6.322 
4.218 

Day    8 

5.879 
2.441 

Day  13 
3.055 

2.441 
Day  18 

2.709 
2. Ml 

Day  23 

2.709 
2.441 


Day    4 

5.758 
3.443 

Day    9 

3.728 
2.441 

Day  14 
3.139 

2.441 

Day  19 
2.945 
2.441 

Day  24 

2.636 
2.441 


Days  Required 

to  Relearn 

8.00 

5.00 


Day    5 

6.279 
3.400 

Day  10 

3.109 
2.441 

Day  15 
3.073 
2.441 

Day  20 

2.848 
2.441 

Day  25 
to  50 

2.636 
2.441 


TABLE    VId 

THE  INCLINED  PLANE 

ANATOMICAL  DATA  OF  SEVENTH  AND  EIGHTH  GENERATION  INBRED  RATS 

Body 

Length 

in  mm. 

Seventh  Average 202. 13 

Eighth  Average 189 . 73 

Water 

in  Cord, 

per 

cent 

Seventh  Average 71 . 569 

Eighth  Average 71 .304 


Body 

Weight 
in  grms. 
201.44 
167.33 

Brain 
Weight 
in  grms. 
1.72868 
1.71299 

Cord 
Weight 
in  grms. 
.54607 
.52967 

Water 
in  Brain, 
per  cent 
78.542 
78.185 

Per  cent 
Brain  Weight 
in  Relation  to 
Body  Length 
.85622 
.90323 

Per  cent 
Brain  Weight 
in  Relation  to 
Body  Weight 
.90560 
1.05218 

Age 
killed, 
Days 

223 

217 

In  Plate  X  is  shown  the  curve  of  learning  (below)  and  of  re- 
learning  (above)  of  the  seventh  generation  of  inbred  rats  compared 
with  those  of  the  eighth.  These  curves  are  constructed  from 
figures  given  in  Table  VI.  The  curve  of  the  seventh  generation 
rats  is  indicated  by  the  broken  line,  that  of  the  eighth  generation 


42 


GARDNER 'CHENEY  BASSET 


by  the  solid  line.  The  ordinates  show  the  average  daily  time 
in  seconds  for  each  group,  and  the  abscissae  the  number  of  the 
day  in  which  such  time  was  made.  Both  curves  in  the  learning 
series  are  very  irregular,  especially  so  that  of  the  eighth  genera- 
tion rats.  Although  irregular,  the  seventh  generation  curve  lies 


fi.St)  JB.Jil 


Plate  X 
The  Inclined  Plane 


below  that  of  the  eighth  except  in  a  few  instances.  From  the 
first,  the  relearning  curves  are  similar  and  very  regular,  although 
the  eighth  generation  curve  remains  below  that  of  the  seventh 
all  the  way.  But  both  of  the  relearning  groups  are  selected, 
four  of  the  seventh  and  seven  of  the  eighth  generation  having 
failed  to  learn  the  inclined  plane. 


HABIT  FORMATION  IN  ALBINO  RATS  43 

VI.     SUMMARY  AND  CONCLUSIONS 

During  a  series  of  experiments  in  inbreeding  conducted  at  the 
Wistar  Institute  of  Anatomy  and  Biology,  a  strain  of  albino 
rats  was  produced,  the  relative  brain  weights  of  which  averaged 
considerably  less  than  normal.  Whether  such  a  condition  was 
induced  by  the  inbreeding  or  was  due  to  environmental  factors 
can  not  be  stated  with  certitude  at  the  present  time.  Inbreeding, 
per  se,  may  not  be,  necessarily,  productive  of  deleterious  results 
if  the  parent  stock  be  perfect  in  every  respect ;  but  it  is  impossible, 
by  any  means  at  our  command,  to  determine  physical  perfection 
in  any  organism.  An  environmental  factor  that  may  have  had 
some  bearing  on  the  lesser  relative  brain  weight  condition  of  the 
two  strains  of  rats  (A  and  B)  used  in  these  experiments  was,  that 
after  four  generations  of  inbreeding  the  rats  did  not  appear  to 
thrive ;  at  that  time  a  change  of  diet  took  place,  after  which  they 
seemed  in  better  health. 

The  writer  spent  two  years  in  the  task  of  attempting  to  ascer- 
tain whether  or  not  the  less  than  normal  relative  brain  weight 
was  accompanied  by  a  corresponding  lesser  ability  to  form 
habits,  and,  also,  if  such  ability  was  progressively  less  from  one 
generation  of  inbreeding  to  the  next.  There  were  used  in  all  the 
experiments  one  hundred  and  twenty-four  rats:  sixty-two 
inbreds  and  sixty-two  normal  controls.  An  equal  number  of 
males  and  females  from  inbreds  and  controls  were  used  in  each 
experiment.  Plate  XI  shows  the  distribution  of  relative  brain 
weights  (with  reference  to  body  length)  of  the  inbred  rats  and  of 
the  normal  control  series.  The  inbred  distribution  is  represented 
by  the  lower  curve,  that  of  the  normal  control  by  the  upper. 
The  greatest  frequency  in  the  inbred  curve  occurs  at  .88%;  in 
the  normal  curve  at  .92%.  The  entire  inbred  distribution  is 
from  .70%  to  .95%;  that  of  the  normal  controls  from  .84%  to 
1.05%.  The  average  relative  brain  weight  (with  reference  to 
body  length)  of  the  sixty-two  normal  control  rats  is  .93351%; 
that  of  the  inbreds  is  .87335%,  or  6.44%  less  than  that  of  the 
normal  control. 

In  order  to  compare  the  ability  of  the  rats  of  the  lesser  brain 
weight  strain  (inbred  rats)  with  a  normal  control  series,  three 
experiments  were  used: 

1.  The  Maze,  in  which  all  the  rats  used  were  given  five  trials 
daily  until  they  had  learned  perfectly,  or,  failing  to  learn,  had 


44 


GARDNER  CHENEY  BASSET 


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Q 


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LL 


HABIT  FORMATION  IN  ALBINO  RATS  45 

worked  one  hundred  days  (500  trials).  At  the  expiration  of 
sixty  days  after  perfect  learning  the  rats,  except  those  failing  to 
learn,  were  tested  for  absolute  retention  and  relearning  until 
relearning  was  perfect,  or,  failing  relearning,  for  fifty  days  (250 
trials). 

2.  The  Preliminary  Inclined  Plane,  in  which  all  the  rats  used 
were  given  five  trials  daily  for  twenty  days  (100  trials);    at  the 
expiration  of  sixty  days  after  this  period  they  were  all  tested  for 
absolute  retention  and  relearning  for  a  period  of  five  days  (25 
trials). 

3.  The  Inclined  Plane,  in  which  all  the  rats  used  were  given 
three  trials  daily  until  they  had  learned  perfectly,  or,  failing  to 
learn,  had  worked  one  hundred  days  (300  trials).     At  the  ex- 
piration of  sixty  days  after  perfect  learning  the  rats,  except  those 
failing  to  learn,  were  tested  for  absolute  retention  and  relearning 
until  relearning  was  perfect. 

In  all  these  experiments  the  strain  of  rats  of  lesser  relative 
brain  weight  (the  inbreds)  learned  less  well,  on  the  average,  than 
the  normal  control  series.  In  the  maze  and  inclined  plane  ex- 
periments the  average  number  of  days  required  to  learn  and  re- 
learn,  and  the  time  of  absolute  retention,  was  far  greater  in  the 
case  of  the  inbred  rats  than  in  that  of  the  normal  control  series. 
In  the  maze  experiment,  two  inbreds  and  one  control  failed  to 
learn;  two  inbreds  failed  to  relearn.  In  the  inclined  plane  ex- 
periment, eleven  inbreds  and  two  controls  failed  to  learn. 

The  similarity  of  behavior  of  the  control  rats  containing  blood 
of  the  B  strain  to  that  of  the  inbreds  suggests  the  importance 
of  crossing  a  strain  of  inbred  rats  of  lesser  brain  weight  with  normal 
rats,  and  carrying  out  a  series  of  tests  such  as  have  been  presented 
in  this  paper,  with  two  controls :  one  of  normal  rats,  and  one  of 
rats  of  lesser  relative  brain  weight. 

In  the  maze  experiment  the  inbred  rats  of  the  seventh  genera- 
tion did  a  little  less  well  than  those  of  the  sixth.  In  the  inclined 
plane  experiment  the  rats  of  the  eighth  generation  did  a  little 
less  well  than  those  of  the  seventh.  It  would  seem  (although 
lessening  of  relative  brain  weight  had  ceased  after  the  fourth 
generation  of  inbreds)  that  the  ability  to  form  habits  lessened  pro- 
gressively with  successive  generations  of  inbreeding. 

The  writer  had  intended  to  attempt  a  correlation  (if  any 
existed)  between  the  number  of  days  required  to  learn  a  habit 


46  GARDNER  CHENEY  BASSET 

and  the  number  of  days  required  to  relearn  after  sixty  days' 
rest.  But  most  of  the  rats  relearned  very  quickly  without 
reference  to  trie  number  of  days  required  for  learning ;  in  numbers, 
too,  the  rats  were  too  few  for  such  mathematical  consideration. 
An  investigation  along  such  a  line  should  consist  of  but  one 
relatively  simple  experiment;  several  hundred  rats  of  one  sex 
only  should  be  used;  and  the  period  of  time  between  the  corii- 
pletion  of  learning  and  the  beginning  of  relearning  should  be 
lengthened  to,  at  the  least,  ninety  days. 

The  general  results  of  the  experiments  here  set  forth  may  be 
summed  up  as  follows:  On  the  average,  the  strain  of  inbred  rats 
having  a  less  than  normal  relative  brain  weight  did  less  well  in 
learning  to  form  habits  than  did  the  normal  control  series. 

From  these  results  the  following  may  be  formulated:  A  less 
than  normal  brain  weight  in  a  strain  of  rats  is  accompanied  by  a 
less  than  normal  ability  to  form  habits. 

ADDENDUM 

The  tables  of  individual  daily  averages,  from  which  the  tables 
of  group  averages  contained  in  this  monograph  are  derived,  are 
so  extensive  as  to  preclude  publication.  If,  however,  any  may  be 
interested  in  them,  the  original  copy  is  deposited  with  the  library 
of  the  Wistar  Institute  of  Anatomy  and  Biology,  Philadelphia, 
Pennsylvania;  and  a  duplicate  is  in  the  private  library  of  the 
author'. 


VITA 

Gardner  Cheney  Basset  was  born  in  Boston,  Massachusetts, 
June  17,  1873.  He  received  his  elementary  and  secondary  edu- 
cation in  the  public  schools  of  Boston  and  Newton,  Massachu- 
setts. From  the  year  1890  to  1908  he  was  in  the  wholesale 
shoe  business,  serving  successively  as  receiving  clerk,  buyer, 
traveling  salesman  and  superintendent.  He  entered  the  Col- 
legiate Department  of  Clark  University  in  1908;  was  assistant 
in  Biology  during  the  year  1909-1910;  assistant  in  Psychology 
during  the  year  1910-1911;  and  in  1911  he  received  the  degree 
of  Bachelor  of  Arts  with  highest  honor.  He  spent  the  summer 
of  1910  at  Cornell  University  in  the  study  of  Experimental 
Psychology.  In  October,  1911,  he  entered  the  Johns  Hopkins 
University,  and  was  appointed  University  Fellow  in  that  insti- 
tution for  the  year  1912-1913. 

While  at  the  Johns  Hopkins  University  Mr.  Basset  studied 
Psychology  under  Drs.  Watson  and  Dunlap,  Psychiatry  under 
Dr.  Meyer,  Genetics  under  Dr.  Jennings,  and  Neurology  under 
Drs.  Mall  and  Sabin. 


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